Thermally-assisted magnetic recording device, thermally-assisted magnetic reproducing device and electron beam recorder

ABSTRACT

Electrons are directed from an electron emitter towards a magnetic recording medium to heat a recording portion of the magnetic recording medium and magnetic information is written by a magnetic recording head to the temperature-elevated recording portion. Otherwise, a magnetic head having a magnetic pole is used and the magnetic pole serves as an electron emitter as well. Alternatively, a space between the electron emitter and recording medium is made shorter smaller the mean free path of electrons in the atmosphere to considerably improve the recording density.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a thermally-assisted recordingand/or reproducing device, and more particularly, to an improved andnovel thermally-assisted recording device capable of heating a magneticor other kinds of recording media by electron beams to write and/or readdata to the medium with an extremely high density.

[0002] Personal computer (PC) systems and audio and/or video (AV)systems require a peripheral storage unit which has a large capacity andalso is inexpensive. Currently, most of such peripheral storage unitsare magnetic or optical recording devices. The magnetic recordingdevices include a fixed magnetic hard disc drive (HDD) and magnetic taperecording device. Many of the PC systems adopt an HDD and an opticaldisc drive or magnetic tape recording device. Generally, various dataincluding OS (operating system) and other software are stored in the HDDto which random access is made, while the optical disc drive or magnetictape recording device is used for long-term storage of important data.Conventionally, the AV systems for storage of a large amount of movingpicture information use mainly the magnetic tape recording device as theperipheral storage unit. With the larger capacity of the recent HDD. andoptical recording device, however, it has become expected that the HDDand optical recording device are employed in the AV systems for theirspeedy accessibility which is not possible with the conventionalmagnetic tape recording device. The magnetic and optical recordingdevices for use in the PC systems and AV systems are required to have alarger capacity and higher speed and be more inexpensive. With theconventional peripheral storage units, however, it is said that problemswill arise as in the following.

[0003] First, the magnetic recording device will be considered. Themagnetic recording device to magnetically write and read information hasconstantly been evolved as a large capacity, high speed and inexpensiveinformation storage means. Among others, the recent hard disc drive(HDD) has shown remarkable improvements. Specifically, as proved on theproduct level, its recording density is over 10 Gbpsi (gigabits persquare inch), internal data transfer rate is over 100 Mbps (megabits persecond) and price is as low as several yens/MB (megabytes). The highrecording density of HDD is due to a combination of improvements of aplurality of elements such as signal processing technique, servo controlmechanisms, head, medium, HID, etc. Recently, however, it has becomeapparent that the thermal agitation of the medium inhibits the higherdensity of HDD.

[0004] The high density of magnetic recording can be attained by makingsmaller the recording cell (recording bit) size. However, as therecording cell is made smaller, the signal magnetic field intensity fromthe medium is reduced. So, to assure a predetermined signal-to-noiseratio (S/N ratio), it is indispensable to reduce the medium noise. Themedium noise is caused mainly by a disordered magnetic transition. Themagnitude of the disorder is proportional to a magnetic transition unitof the medium. The magnetic medium uses a layer formed frompolycrystalline particles (will be referred to as “multiparticle layer”or “multiparticle medium” herein). In case a magnetic exchangeinteraction works between magnetic particles, the magnetic transitionunit of the multiparticle layer is composed of a plurality ofexchange-coupled magnetic particles.

[0005] Heretofore, when a medium is to have the recording density isseveral hundreds Mbpsi to several Gbpsi for example, the lower noise ofthe medium has been attained mainly by reducing the exchange interactionbetween the magnetic particles and making smaller the magnetictransition unit. In the latest magnetic medium of 10 Gbpsi in recordingdensity, the magnetic transition unit is of only 2 or 3 magneticparticles. Thus, predictably, the magnetic transition unit will bereduced to only one magnetic particle in near future.

[0006] Therefore, to assure a predetermined S/N ratio by furtherreducing the magnetic transition unit, it is necessary to make smallerthe size of the magnetic particles. Taking the volume of a magneticparticle as V, a magnetic energy the particle has can be expressed asKuV where Ku is an anisotropy energy density the particle has. When V ismade smaller for a lower medium noise, KuV becomes smaller with a resultthat the thermal energy each particle has at a temperature near the roomtemperature will disturb information written in the medium, which is the“thermal agitation” referred to herein and has become the problem asmentioned above.

[0007] According to the analysis made by Sharrock et al., the ratiobetween magnetic energy and thermal energy of a particle, KuV/kT where kis Boltzman's constant and t is absolute temperature, is required to begreater than 100 or so in order to keep the reliability of the recordlife. If the particle size is decreased for a lower medium noise withthe anisotropy energy density Ku being maintained at (2 to 3)×10⁶ erg/ccof the CoCr group alloy conventionally used as a magnetic layer in therecording medium, it will be difficult to assure a thermal agitationresistance.

[0008] More specifically, the multiparticle layer of Co, Cr, Ta and Ptused in the current magnetic recording medium has a Ku value of about (2to 4)×10⁶ erg/cc. With a particle size of 10 nmφ−10 nmt or so, themagnetic energy of each particle will be under 100 times of the thermalenergy each particle has at the room temperature and there will takeplace a noticeable destruction of written information due to the thermalagitation. Improvement of the medium material and increasing theanisotropy energy density Ku may look like an approach to the solutionof the problem, but a larger value of Ku will be accompanied by a largercoercive force, which will make the information writing to the mediummore difficult.

[0009] Recently, magnetic layer materials having a Ku value of more than10⁷ erg/cc such as CoPt, FePd, etc. have been attracting much attentionfrom all the field of industries concerned. However, simply increasingthe Ku value for compatibility between the small particle size andthermal agitation resistance will lead to another problem. The problemconcerns the recording sensitivity. Specifically, as the Ku value of themagnetic layer of a medium is increased, the recording coercive forceHc0 of the medium (Hc0=Ku/Isb; Isb is a net magnetization of themagnetic layer of the medium) will increase and the necessary magneticfield for saturation recording increase proportionally to Hc0.

[0010] A recording magnetic field developed by a recording head andapplied to the medium depends upon a current supplied to a recordingcoil as well as upon a recording magnetic pole material, magnetic poleshape, spacing, medium type, layer thickness, etc. Since the tip of therecording magnetic pole is reduced in size as the recording density ishigher, however, the magnetic field developed by the recording head islimited in intensity.

[0011] Even a combination of a single-pole head which will develop alargest magnetic field and a vertical medium backed with a soft magneticmaterial for example can develop a magnetic field whose largest possibleintensity is on the order of 10 kOe (Oe: oersted). On the other hand, toassure a sufficient thermal agitation resistance with a necessaryparticle size of about 5 nm for a future high-density, low-noise medium,it is necessary to use a magnetic layer material having a KU value of10⁷ erg/cc or more. In this case, however, since the magnetic fieldintensity necessary for write to the medium at a temperature approximateto the room temperature is over 10 kOe, no write to the medium ispossible. Therefore, if the Ku value of the medium is simply increased,there will arise a problem of the write to the medium being impossible.

[0012] As having been described in the foregoing, in the magneticrecording using the conventional multiparticle medium, the lower noise,thermal agitation resistance and higher recording density are in atrade-off relation with each other, which is an essential factor uponwhich the limit of the recording density depends.

[0013] Secondly, the optical recording device will be considered. A highdensity of the optical recording basically depends upon the reduction ofthe size of a laser spot focused on an optical recording medium.Therefore, for a higher recording density with the optical recordingdevice, a laser light used should be of a shorter wavelength or anobjective lens used should have a higher numerical aperture (NA).However, use of a laser light having a shorter wavelength is limited byselection of a laser element material for use with the laser light andalso by the spectral transmittances of the substrate of an optical discand various optical elements included in the optical system of theoptical recording device. Recently, there has been proposed a ultra-highdensity optical recording using a near-field light (evanescent wave).For practical use of the near-field light, however, there are manyproblems to solve since the light spot size and light intensity on themedium are theoretically in a trade-off relation with each other.

[0014] Therefore, it is predicable that in organizing a futureperipheral storage unit having a recording density of over Tb(terabits)/inch², both the conventional magnetic and optical recordingsystems will encounter many difficulties.

SUMMARY OF THE INVENTION

[0015] Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks of the prior art by providing a magneticrecording device having a novel construction based on a differentprinciple from that for the conventional magnetic recording devices andcapable of recording at a dramatically high density.

[0016] The present invention has another object to provide an electronbeam recording device capable of solving the thermal agitation problemin the magnetic recording and trade-off problem related to thenear-field light used in the optical recording to break through therecording density limit of the conventional peripheral storage units.

[0017] The Inventors of the present invention propose athermally-assisted magnetic recording device based on a novel concept toattain the above object. In this thermally-assisted magnetic recordingdevice, magnetic particles so fine that noise therefrom is sufficientlysmall are used and a recording layer having a high anisotropy energydensity (Ku) at a temperature near the room temperature is used toassure a thermal agitation resistance. In a medium having such a largeKu value, since the magnetic field intensity necessary for recordingexceeds the intensity of a magnetic field developed by the recordinghead when the ambient temperature is near the room temperature, norecording is possible. However, by locally heating the recording mediumby any means, the coercive force Hc0 of the temperature-elevated portionof the medium can be reduced to below the magnetic field intensity ofthe recording head to write information to the medium.

[0018] The recording medium may be heated by irradiating light beam tonear the recording magnetic pole. By locally heating the medium with thelight beam during recording, the Hc0 value of the temperature-elevatedportion of the medium can be reduced to below the intensity of themagnetic field developed by the recording head, thereby permitting towrite information to the medium.

[0019] When a light beam from a conventional light source is used as aheat source, however, since the size of light spot is defined by thediffraction limit, an area of several hundreds of nm or more will beheated. Thus, use of such a light beam is not suitable for a futuremagnetic recording in which the track width will be 100 nm or less.Also, a near-field light may be used in order to limit the light beam toless than the diffraction limit. However, a near-field light emittedfrom a conventional light source cannot be used efficiently and thereduction in area of the temperature-elevated portion and light beampower are in a trade-off relation with each other, thus no sufficientheating can be assured in a recording at a high density.

[0020] That is, in the modality in which a far-field light is used as aheat source, the light spot size is defined by the diffraction limit, sono heating of a fine area is possible. On th other hand, the near-fieldlight cannot be used with a high efficiency, and thus sufficient heatingis difficult in a higher density of recording.

[0021] To avoid the above problem, the present invention uses anelectron beam as a heat source.

[0022] Namely, the above object can be attained by providing athermally-assisted magnetic recording device including, according to thepresent invention, an electron emission source of electron emitter and amagnetic recording head, electrons being directed from the electronemitter towards the magnetic recording medium to heat a recordingportion of the magnetic recording medium and magnetic information beingwritten to the temperature-elevated recording portion by the magneticrecording head applying the recording magnetic field to the magneticrecording medium. The electron beam can be limited very easily to a veryfine spot size, whereby the recording density can. considerably beimproved.

[0023] In the above thermally-assisted magnetic recording deviceaccording to the present invention, the electron emitter can heat themagnetic recording medium so that the coercive force of the recordingportion of the magnetic recording medium will be smaller than theintensity of the recording magnetic field developed at the recordingportion by the magnetic recording head. Thus, positive recording ispossible to a recording medium having a large coercive force.

[0024] Also in the above apparatus, the recording portion of themagnetic recording medium has a larger coercive force than the intensityof the magnetic field developed by the magnetic recording head, at thenormal temperature. This magnetic recording medium is strong against thethermal agitation and the size of recording cells can be made rathersmaller than the recording cell size in the conventional magneticrecording medium.

[0025] Further, in the above apparatus, there is provided a drivingmechanism to move a recording surface of the magnetic recording mediumin relation to the electron emitter and magnetic recording head, andafter the magnetic recording medium is moved by the driving mechanism,the electron emitter will come nearer to a leading position in relationto the recording surface than the magnetic recording head. Thus, it ispossible to positively elevate the temperature of the recording portionof the magnetic recording medium prior to recording.

[0026] Also in the above apparatus, the electron emitter includes aplurality of electron emitters disposed along the direction of themovement thereof by the driving mechanism. Thus, the recording portionof the magnetic recording medium can positively be heated.

[0027] Moreover in the above apparatus, there are formed on the magneticrecording medium a recording track parallel to the moving direction; thelength Te of the electron emitter in the width direction of therecording track and length Tw of the magnetic recording head in thewidth direction of the recording track are in a relation of Te/2≦Tw≦2Tewith each other.

[0028] Moreover in the above apparatus, the electron emitter emitselectrons by field emission. Thus, fine electron beam can positivelygenerated, and the electron emitter has an improved reliability andoperating life.

[0029] Also in the above apparatus, the electron emitter is placed in anon-oxidizing atmosphere or depressurized atmosphere. Thus, the electronemitter has a further improved reliability and service life.

[0030] In the above respect, the oxygen partial pressure density X (inmols/cm³) and emission electron current density J (in A/cm²) of theelectron emitter are in relations of X≦1.25×10¹²×J and J≦10⁴ with eachother.

[0031] In the thermally-assisted magnetic recording according to thepresent invention, an electron emitter is used as a heat source. Theelectron emitter may be any of various types such as field emissiontype, thermoelectronic emission type, photoemission type, tunnelelectron emission type, etc. The “field emission type” is such that byproviding a high potential gradient (electric field) on an electronemission surface, electrons are directly emitted from the surface. Thepresent invention adopts a field emission type electron emitter. In thiscase, since the electron emission area is on the order of 10 nm, an areaof about 10 nm of the medium can easily be heated, thus the presentinvention can attain a resolution much better than that of theconventional method using the light beam. Also in case an electronemitter of the thermoelectronic emission type is used, however, thenearly same effect can be assured by converging the electron beam to apredetermined size.

[0032] Normally, the electron beam is used under a vacuum. However,taking in consideration the facts that the spacing between the magnetichead and medium is several tens of nm or less and this spacing willfurther be reduced in future and that the mean free path of electrons at1 atm. is on the order of 150 nm which is sufficiently longer than thespacing between the magnetic head and medium, it can be said thatemitted electron beam can be directed towards the medium with nocollision. Namely, the electron emitter can be installed in a magneticrecording device which is to be used at normal atmospheric pressure.

[0033] Note that the mean free path of electrons depends upon the typeof gas and electron energy. However, in case the gas used is a nitrogenbeing one of the major elements of air, the mean free path of electronswill be shortest even when the electron energy is 2 eV or so. The meanfree path, in the nitrogen at atmospheric pressure, of the electronhaving the energy of 2 eV is 150 nm. Also, in case the gas used isoxygen being another major element, the mean free path of electrons isshortest when the electron energy is on the order of 20 eV. However, themean free path is 300 nm or more, which is long enough as compared withthe above-mentioned spacing.

[0034] Further, when the electron beam is used in a depressurizedatmosphere according to the present invention, the probability ofcollision before an electron beam is incident upon the medium can besaid to be rather low. Also, in case the gas used is an inert gasatmosphere according to the present invention, when it is a drynitrogen, the mean free path of electrons is a minimum of 150 nm or soas in the above. When a rare gas such as Ne, Ar, Kr or Xe is used, theminimum value of mean free path of electrons at 1 atm. is 1000, 160, 130or 94 nm, which is long enough as compared with the above spacing. Theelectrons can be incident upon the medium with little collision.

[0035] An inert gas atmosphere at a substantial atmospheric pressureshould preferably be charged in the recording device for a longerservice life of the electron emitter. When dry nitrogen is used as theinert gas, the mean free path of electrons is a minimum of 150 nm or so.Also when a rare gas such as Ne, Ar, Kr or Xe is used, the mean freepath of electrons is long enough as in the above. In case, with thespacing between the magnetic head and medium being of several tens ofnm, the electron beam can substantially work as under a vacuum. In thisway, use of the dry nitrogen or rare gas atmosphere can permit a stableperformance of the electron beam.

[0036] Also, the pressure of the atmosphere in which the electron beamis used may be near, higher or lower than 1 atm. However, a pressure ofthe atmosphere being at a substantial atmospheric pressure is convenientfrom the practical viewpoint.

[0037] On the assumption that the pressure inside the apparatus is P (inTorr), the minimum value of the mean free path of electrons at 1 atm. isλmin (in nm) and the spacing between the electron emitter and medium isd (in nm), the present invention should desirably meet the followingcondition:

d<λmin×(760/P)

[0038] The minimum value of mean free path of electrons λmin is definedto a mean free path over which there will take place no collision with aprobability of 1/e (e is a base of natural logarithm) when the electrontravels over the distance of λmin. That is, when the conditiond<λmin×(760/P) is met, the electron will collide with molecules with aprobability of about 63% in the course since it is emitted untilincident upon the medium. More preferably, the following conditionshould be met:

d<(⅓)×λmin×(760/P)

[0039] When the above condition is met, the collision probability can bereduced to less than ½. It is more desirable to use a coefficient of ⅕in place of the coefficient of ⅓ in the above expression. With thiscoefficient, the collision probability can be reduced to so small avalue as will not be inconvenient in practice.

[0040] The pressure P inside the apparatus falls within a substantialrange of the atmospheric pressure. Within a range meeting the abovecondition, it may be selected depending upon whether a practicalapparatus is feasible with the lower limit of the pressure P. If thepressure inside the apparatus is different from the atmospheric pressureor if the apparatus is charged with a gas different from the atmosphere,a hermetic enclosure is required.

[0041] In case the hermetic enclosure is used, the lower limit of thepressure P depends upon the mechanical strength of the enclosure as thecase may be. In case of the conventional electron beam recording deviceunder a vacuum, since the enclosure is applied with a pressure as highas 1 kg/cm², it is not easy to assure a sufficient mechanical strengthof the enclosure and also to maintain the vacuum state.

[0042] According to the present invention, however, the lower limit ofthe pressure P can be selected depending upon the practically allowablepressure to the enclosure and vacuum sealing of the enclosure. Since thelower limit of the pressure P should be considered in designing theenclosure, it cannot be fixed to a general value. However, a half or soof the atmospheric pressure may be reasonable. When the lower limit ofthe pressure P is higher than the half of the atmospheric pressure, thepressure applied to the enclosure will be 0.5 kg/cm² or so and thesealed or hermetic extent of the enclosure may be a sealing provided bythe ordinary aluminum sash for example.

[0043] The upper limit of the pressure P is basically defined by theabove expression. The practical upper limit is double the atmosphericpressure or so based on the same consideration to the lower limit. The“substantial atmospheric pressure” referred to herein is as having beendescribed in the foregoing.

[0044] Now, the electron emitter of the field emission type will beconsidered. The electron emission area of this source depends in sizeupon the applied electric field and shape of the electron emitter. Thesize of the electron emission area is on the order of 10 nm when theelectric field is 10⁶ to 10⁷ V/cm and the electron emitter has asharpened or tapered shape obtained by a selective etching or whose endcurvature is several tens of nm or less. This size is difficult torealize with a light beam and the electron emitter should preferably beapplied to a future magnetic recording device in which recording cellsize is several tens of nm. Emission current depends on the appliedelectric field. With an electric field of 10⁶ to 10⁷ V/cm, an emissioncurrent of about 10⁻⁶ to 10⁻⁴ A can be obtained from an area of 10 nm indiameter.

[0045] Note that the emission current is nearly proportional to thesquare of the intensity of applied electric field according to theFowler-Nordheim expression. Therefore, if the electric field intensityis 3.3×10⁷ V/cm for example, the emission current can be 10⁻³ A.Although an electric field intensity of 10⁶ to 10⁷ V/cm may seem to bevery high, it will be suitably applicable to the magnetic recordingdevice since the voltage to be applied between the electron emitter andmedium is a maximum of several volts to several tens of V because theabove spacing is several tens of nm.

[0046] Next, the mechanism of heating of the medium by electron beamwill be described. When a voltage of 10 V is applied (with the spacingbeing 10 nm and field intensity being 10⁷ V/cm), an emission current of10⁻⁴ A will provide a power of 10⁻³ W. When a voltage of 33 V is applied(with the spacing being 10 nm and field intensity being 3.3×10⁷ V/c), anemission current of 10⁻³ A will provide a power of 3.3×10⁻² W. When thispower is applied to a square area on the medium, whose one side is 10 nmlong, the power density will be 10⁹ W/cm² or 3.3×10¹⁰ W/cm². When 10 m/sis used as a practical linear velocity (moving speed of the medium inthe direction of the recording track) in the magnetic disc drive, themedium takes a time of 1 ns for passing by the heated area of 10 nm.Therefore, the energy density applied to the square area whose one sideis 10 nm long will be 1 J/cm² or 33 J/cm². It will be consideredherebelow whether this value is adequate for heating the medium.

[0047] As an example of the heating mechanism using an electron beam,there is available a heating mechanism in which the electron beambehaves as de Broglie wave to heat the medium. The de Broglie wave is onthe order of 0.4 nm when the electron energy is 10 V while it is about0.2 nm when the electron energy is 33 V. Namely, it is equal to the atomsize, so a lattice vibration (heating) can be generated. Alternatively,there may be available a mechanism in which an electron beam having suchan energy is incident upon the medium to oscillate and excite theplasmon, and an energy emitted when the plasmon-oscillated electron andpositive hole in pair are recombined is given to a phonon, namely, to alattice to induce a lattice vibration, that is, a heat.

[0048] The power density or energy density necessary for heating themedium can be considered to be nearly equal to that used with theoptical disc. So, if the above power density 10⁹ W/cm² or 3.3 ×10¹⁰W/cm², or energy density 1 J/cm² or 33 J/cm², is equal to or larger thanthe power density or energy density used with the optical disc, themedium can be heated sufficiently with the electron beam. In a commonphase-change disc, for example, a linear velocity of 6 m/s, full widthat half maximum (FWHM) of 0.6 μm of the light spot and a recording powerof 10 mW will permit to heat this medium to a higher temperature thanits melting point (600° C.). Since the medium takes a time of 100 ns forpassing by the full width at half maximum and the area of the light spotis 0.28×10⁻⁸ cm², the power density will be 3.5×10⁶ W/cm² and energydensity will be 0.35 J/cm². Therefore, it can be said that the mediumcan sufficiently be heated by the plasmon oscillation with a energydensity of 1 J/cm².

[0049] In addition, there can take place a Joule-heating mechanism inwhich the electron beam causes a current to flow through the mediumwhich is thus heated by the Joule-heating. This mechanism will coexistwith the above-mentioned plasmon-oscillation heating mechanism.Comparison with the power density used with the optical disc will leadto the understanding of the reason why the Joule-heating mechanism issuitable for heating the medium. Specifically, when a current of 10⁻⁴ Aor 10⁻³ A is supplied to a square area whose one side is 10 nm long ofthe medium in the direction of the layer thickness, the heating powerwill be R×10⁻⁸ W or R×10⁻⁶ W where R is a resistance of the medium. Whenthe resistivity of a magnetic recording medium or magneto-opticalrecording medium is (5 to 6)×10⁻⁶ Ωcm, the area of current path is 10⁻¹²cm² (10 nm square) and the current path length, namely, magnetic layerthickness is 2×10⁻⁶ cm (20 nm), the resistance of the medium will be 10Ωor so. Therefore, the heating power will be 10⁻⁷ W or 10⁻⁵ W. Divisionof this heating power by the heated area of 10⁻¹² cm²) provides 10⁵W/cm² or 10⁷ W/cm². Since the time of current supply is different fromthe time of electron beam incidence, the Joule-heating mechanism shouldbe considered by comparison in power density, not in energy density.Thus, it can be said that the current of 10⁻⁴ A will be somewhatinsufficient, but 10⁻³ A will enable a sufficient Joule heating.

[0050] Actually, there will take place together, as mentioned above, theprocess in which the medium is heated by the plasmon oscillation andexcitation and the process in which the medium is heated by the Jouleheating due to the current supply to the medium. In any of the aboveprocesses, the power density and energy density are sufficient.Therefore, any of these heating mechanisms may be selected for use inthe thermally-assisted magnetic recording device according to thepresent invention.

[0051] The thermally-assisted magnetic recording head according to thepresent invention should preferably be embodied as a one in which anelectron emitter and recording magnetic pole are disposed in this orderfrom the downstream (leading) side in the direction of the mediummovement. Owing to this arrangement, a recording magnetic. field can beapplied to the medium at a position where Hc0 has become sufficientlylow immediately after the medium is heated by the electron beam. Thedistance between the electron beam incident position and recordingmagnetic field-applied position depends upon the thermal response of themedium as well, but should preferably be 100 nm or less, and morepreferably be several tens of nm or less.

[0052] For a higher efficiency of the heating, a plurality of electronemitters in the electron emitter should be disposed in the direction ofthe recording track. The size of the heated area should preferably benearly equal to the width of the recording track to enable auniformmagnetic transition over the trackwidth. Also the track width Teof the electron emitter, and track width Tw of the recording head shoulddesirably meet the condition of Te/2≦Tw≦2Te.

[0053] The inside of the ordinary magnetic disc drive communicates withthe ambient atmosphere. When the electron beam is to be used in anatmosphere containing oxygen and moisture, consideration should be givento the life of the electron emitter as well as to the mean free path ofelectrons. At atmospheric pressure, air molecules or water molecules inthe atmosphere will be adsorbed by the electron emitter and willpossibly shorten the service light of the latter. Different from theconventional thermal emission type electron beam emitter and photoemission type electron beam emitter, the field emission type electronbeam emitter having actively been researched and developed recently isextremely resistant against adsorbed molecules. When carbon (C) is usedas a material for the electron emitter, the latter will be lessinfluenced by the oxidation. For a practically long service life of theelectron emitter, however, the densities of the gas atmosphere near theemitters, especially, the densities of oxygen, water and theirdissociated species, and the frequency of their incidence upon theemitters, should be kept low.

[0054] The Inventors of the present invention made many experimentsmainly on STM (scanning tunneling microscopy) emitter, and found fromthe experiment result a emitter-surrounding atmosphere required forobtaining a field emission current stably. As will further be describedlater concerning the embodiments of the present invention, the Inventorof the present invention found that it depends upon the emitter materialhow the emitter-surrounding atmosphere should be and that also whensilicon (Si) on which a surface oxide film is easy to develop was used,electrons could be emitted stably if the density X (mols/cm³) of oxygenmolecules in the emitter-surrounding atmosphere and current density J(in A/cm²) of electrons emitted from the emitter met the condition ofX≦1.25×10¹²×J with J≧10⁴. The definition of the range of J as in theabove condition is intended to present a necessary range of J forsignificantly heating the medium. There will be no sense in defining anemission current with which no significant heating will take place or arelation between X and J which would be when the emitter stopsoperating.

[0055] When the emitter stops operating, a natural oxide layer or aphysical adsorption layer will develop on the emitter surface. When theabove defined condition in the present invention is met, such layerswill easily desorb the emitter surface due to the following operation ofthe emitter. The above definition of the relation between X and J in thepresent invention is intended to present a condition under which so longas an emission current capable of significantly heating the medium issupplied, the tip of the emitter will not be deteriorated due to attackby oxygen. The relation between X and J has a physical meaning thatwhile a hundred electrons are being emitted from the emitter, one oxygenmolecule will be incident upon the emitter surface. With such an extentof the incidence of oxygen molecule, heating of the emitter surface bythe electron emission, etc. will allow the incident oxygen to re-desorbthe emitter surface which will thus not be deteriorated, which is one ofthe findings of the above Inventors' experiments.

[0056] As having been described in the foregoing, according to thepresent invention, a low-noise multiparticle medium formed from veryfine particles, necessary for a high density magnetic write and read,can be made to have a sufficiently high resistance against the thermalagitation at a temperature near the room temperature, and the coerciveforce of the medium, that is, a necessary magnetic field for a magnetictransition, is reduced by incidence of an electron beam upon a portionof the medium to which a recording magnetic field is applied, to therebyenabling a practical recording head to attain a high speed of recording.

[0057] Also, according to the present invention, an electron emitter andwrite and read elements are formed integrally with each other to providea compact and lightweight thermally-assisted magnetic recording head,which will enable a high speed seek operation and inexpensive head anddrive.

[0058] Further, according to the present invention, it is possible toimprove to a practical level the service life of the electron emitter ofa thermally-assisted magnetic recording device in which a medium isheated by a high resolution, high efficiency electron emitter, thecoercive force of the heated portion of the medium is reduced and arecording magnetic field is applied to the portion whose coercive forcehas thus been reduced, thereby recording information to the medium.

[0059] On the other hand, according to the present invention, a magneticpole or magnetic yoke can also be used as an electron emitter, therebyenabling a magnetic write and read with a further high recordingdensity.

[0060] Also according to the present invention, an electron emitterhaving an extremely superior recording resolution to that of the lightbeam or magnetic recording head used in the conventional magneticrecording device, can be used to write information to a medium. Thus,according to the present invention, there can provided a practicalmagnetic recording device in which information can be recorded with aconsiderably improved density and an electron beam recording can be donein the atmosphere, which is impossible with the conventional electronbeam recording.

[0061] That is, according to the present invention, there can beprovided a thermally-assisted magnetic recording device realizing a newconcept that information can be recorded with a drastically higherdensity than with the conventional recording device. Thus the presentinvention is very advantageous in the field of art.

[0062] These objects and other objects, features, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments of the present invention whentaken in conjunction with the accompanying drawings. It should be notedthat the present invention is not limited to the embodiments but canfreely be modified without departing from the scope and spirit thereofdefined in the claims given later.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will be understood more fully from thedetailed description given herebelow and from the accompanying drawingsof the preferred embodiments of the invention. However, the drawings arenot intended to imply limitation of the invention to a specificembodiment, but are for explanation and understanding only.

[0064] In the drawings:

[0065]FIGS. 1A and 1B show the construction of an embodiment of thethermally-assisted magnetic recording head according to the presentinvention, in which FIG. 1A is a lateral sectional view that shows themajor components including the head and recording elements of the headand FIG. 1B is a view from the medium surface of the major recordingelements of the head;

[0066]FIGS. 2A through 2E provide sectional views, enlarged in scale, ofthe-head near the electron emitter, showing steps of manufacturing theelectron emitter;

[0067]FIG. 3 shows an embodiment of the read element which may bedisposed at the leading or trailing side in FIGS. 1A and 1B;

[0068]FIG. 4 graphically shows the temperature characteristic of Hcmeasured with VSM and that of Hc0 estimated using the Sharrock'sexpression;

[0069]FIG. 5 graphically shows a relation between a voltage Ve appliedto the electron emitter and GMR read output voltage Vs per 1 μm of trackwidth in which a current Iw supplied to the recording coil is taken asparameter;

[0070]FIGS. 6A through 6C schematically show the process of recording bythe thermally-assisted magnetic recording head according to the presentinvention, in which FIG. 6A is a sectional view of an portion extractedfrom FIG. 1B and associated with the recording process, FIG. 6Bgraphically shows an electron beam profile on the medium and atemperature distribution on the medium and FIG. 6C graphically shows aspatial distribution of the medium coercive force and that of therecording magnetic field;

[0071]FIG. 7 graphically shows a thermally-assisted magneticcharacteristic of the medium experimentally prepared, in which Hc is acoercive force and Ms is a saturation magnetization related to a readsignal;

[0072]FIG. 8 graphically explains the concept of information recordingto the medium in FIG. 7 according to the present invention;

[0073]FIG. 9 graphically shows the result of the evaluation of the thirdembodiment of the present invention;

[0074]FIG. 10 is a sectional view of the essential components of thethermally-assisted magnetic recording head, by way of example, having aplurality of electron emission tips;

[0075]FIG. 11 is a sectional view of the thermally-assisted magneticrecording head composed of a laminated type magnetic head and electronemitter according to the present invention;

[0076]FIG. 12 is a block diagram of the thermally-assisted magneticrecording device according to the present invention, showing an exampleof the system construction of the recording device;

[0077]FIG. 13 is also a block diagram of the apparatus used in theexperiments conducted by the Inventors of the present invention, showingthe construction of the apparatus;

[0078]FIG. 14 graphically shows a relation between a field emissioncurrent I and voltage V applied to a probe, experienced using two probesmade of Ta (tantalum) and C (carbon), respectively, in a depressurizedatmosphere of 10×10⁻⁴ Pa;

[0079]FIG. 15 graphically shows the result of an experiment effectedusing the probe made of C with the emission current set to 5×10⁻⁵ A;

[0080]FIG. 16 graphically shows a relation between an amount of oxygenin the atmosphere and a time (td) as an index, experienced withdifferent emitters and emission current densities in the experimentwhose result is shown in FIG. 15, the time (td) being a time for whichthe emission current had deteriorated down to 90% (indicated with abroken line) of its initial value;

[0081]FIGS. 17A and 17B are conceptual views of the seventh embodimentof the magnetic recording device according to the present invention,showing especially a means for adjusting the atmosphere inside anenclosure of the magnetic recording device, in which FIG. 17A is aperspective view of the enclosure and FIG. 17B is a sectional view,enlarged in scale, taken along the line X-X′ in FIG. 17A;

[0082]FIG. 18 schematically shows a magnetic recording device disposedin the enclosure shown in FIGS. 17A and 17B, showing the majorcomponents thereof by way of example;

[0083]FIG. 19 is a conceptual sectional view of the major components ofa first magnetic recording head according to the eighth embodiment ofthe present invention;

[0084]FIG. 20 is also a conceptual sectional view showing an exampleconstruction in which the return magnetic pole of a single-pole head isrecessed from the medium-facing surface (air bearing surface);

[0085]FIG. 21 is a conceptual sectional view, enlarged in scale, of aportion, near the air bearing surface, of the main magnetic pole orleading-side magnetic pole of the recording head according to the eighthembodiment of the present invention;

[0086]FIG. 22 is also a conceptual sectional view of the essentialportion of the ring type magnetic recording head according to the eighthembodiment of the present invention;

[0087]FIG. 23 is a conceptual sectional view of the essential potion ofthe magnetic recording device according to the present invention;

[0088]FIG. 24 is a timing chart showing the operations of the magneticrecording device according to the eighth embodiment of the presentinvention;

[0089]FIG. 25 graphically shows the result of evaluation;

[0090]FIG. 26 graphically shows the emission current characteristic;

[0091]FIG. 27 is a conceptual sectional view of the essential portion ofthe magnetic read head according to the ninth embodiment of the presentinvention;

[0092]FIG. 28 graphically shows the magnetic characteristic of a layeror film of a ferrimagnetic alloy (R-T) of amorphous rare earth metal andtransition metal;

[0093]FIG. 29 graphically shows the result of the experiment on theinformation read by the magnetic read head according to the presentinvention;

[0094]FIG. 30 graphically shows the Fowler-Nordheim plotting of the I-Vcharacteristic experienced with the probe made of C (carbon) atatmospheric pressure;

[0095]FIG. 31 graphically shows the collision cross section of electronsin nitrogen (N₂) as a function of the electron energy (Ee);

[0096]FIG. 32 graphically shows the collision cross section of electronsin oxygen (O₂) as a function of the electron energy (Ee);

[0097]FIG. 33 graphically shows the momentum-conversion collision rate(Pc) of electrons in H₂O (water);

[0098]FIG. 34 graphically shows together the result of static write andread test, the field emission current I being indicated along thevertical axis while the voltage pulse time t is indicated along thehorizontal axis;

[0099]FIG. 35 is a conceptual view of the essential portion of therecording head usable in the electron beam recording device according tothe present invention;

[0100]FIG. 36 is a sectional view of an example of the recording mediumusable in the embodiments of the present invention; and

[0101]FIG. 37 is a block diagram of the electron beamrecording/reproducing device according to the present invention, showingan example thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

[0102] Referring now to FIGS. 1A and 1B, there is illustrated in theform of sectional views one embodiment of the thermally-assistedmagnetic recording head according to the present invention. FIG. 1A is alateral sectional view showing the major components including the headand recording elements of the head, and FIG. 1B is a view from themedium surface of the major recording elements of the head. The lineA-A′ in the FIG. 1B corresponds to the center line of a recording track,and a view of the head and medium taken along a line perpendicular tothe center line is FIG. 1A.

[0103] In FIGS. 1A and 1B, the reference S indicates a head substrate, Xa medium moving direction (trailing direction), 10 a recording magneticpole assembly, 11 a main magnetic pole, 12 a return-path magnetic pole,13 a tip of the main magnetic pole, 14 a connection between the mainmagnetic pole 11 and return-path magnetic pole 12, 15 a leading portionof the recording magnetic pole assembly 10, 16 a trailing portion ofthe. recording magnetic assembly 10, 17 a recording magnetic flux, 21 arecording coil, 22 a layer in which the recording coil 21 is buried, 30an electron emitter electrode layer, 40 an electron emitter, 41 anelectron beam, 50 a protective layer, 60 a medium body, 61 a recordinglayer, 62 a soft-magnetic lining layer, 63 an electron beam-incidentportion of the medium 60, 64 a magnetically recording portion of themedium 60, and 65 a magnetization of the medium 60. In the abovestructure, the recording magnetic-pole leading portion 15, recordingmagnetic-pole trailing portion 16 and protective layer 50 are not alwaysnecessary.

[0104] The thermally-assisted magnetic recording head constructed as inthe above can be built following the procedure below:

[0105] First, the head substrate S should preferably be formed fromALTIC (Al, Ti and C) substrate, for example, easy to be work into aslider and which is used to make the ordinary magnetic head. Then theresist frame plating method is used to form the recording magnetic poleassembly 10 directly on the substrate S or on an insulative layerpreviously formed on the substrate S as necessary. The material for themagnetic pole assembly 10 should be a one having a soft-magnetic, highsaturation magnetic flux density, used to form the ordinary magneticrecording element, such as CoNiFe, NiFe or the like. The entirerecording magnetic pole assembly 10 may not always be formed, but onlythe tip 13 of the main magnetic pole 11 may be formed, from the materialhaving the high saturation magnetic flux density.

[0106] After the magnetic pole assembly 10 is thus formed, the layer 22in which the recording coil 21 is to be buried may be etched off withthe resist frame removed. First, the leading portion 15, connection 14between the main magnetic pole 11 and return-path magnetic pole 12 andtrailing portion 16 are formed flat in the recording magnetic poleassembly 10, and then the frame pattern is changed to form the mainmagnetic pole 11 and return-path magnetic pole 12. The main andreturn-path magnetic poles 11 and 12 may be formed to have the sameheight, or the latter may be formed to have a lower height. The tip 13of the main magnetic pole 11 may be worked using a resist frame when thetrack width is relatively large and thus the tip 13 may be formed by thePEP process. In this case, the main and return-path magnetic poles 11and 12 may be formed by collective frame plating with thetrack-directional width of the main magnetic pole 11 made to coincidewith that of the tip 13. If the track width is 100 nm or less, it isdifficult to adopt the PEP process. In this case, a plating is firstmade with the track-directional width of the main magnetic pole 11 madeto coincide with that of the return-path magnetic pole 12, and then theFIB process may be used to determine the track width of the tip 13.

[0107] Next, there is formed on the leading portion 15 of the recordingmagnetic pole pattern, connection 14 and the trailing portion 16 thelayer 22 in which the recording coil 21 is to be buried. On the top ofthe layer 22, there are formed a pattern of the recording coil 21 and apattern of the electron emission electrode layer 30. Then the coil 21and electrode layer 30 are formed by collective plating of copper (Cu).A postprocessing protective coating is provided on exposed resist areasaround the Cu coil 21 and Cu electrode layer 30 as necessary. Thisprotective coating will be the protective layer 50. For electricalconnection between the electrode layer 30 and electron emitter 40, noinsulative layer will be formed on the electrode layer 30.

[0108] Thereafter, the electron emitter will be formed.

[0109]FIGS. 2A through 2E give sectional views, enlarged in scale, ofthe magnetic recording head portion near the electron emitter shown inFIGS. 1A and 1B. The steps of manufacturing the electron emitter will bedescribed herebelow with reference to FIGS. 2A through 2E. Note that inFIGS. 2A through 2E, the elements having the same or similar functionsas or to those of the elements shown in FIGS. 1A and 1B will beindicated with the same or similar reference numerals as those in FIGS.1A and 1B. They will not be described in detail.

[0110] Next to the manufacturing step having been described in the abovewith reference to FIGS. 1A and 1B, a resist 23 is filled up to the topof the recording magnetic pole assembly 10, namely, the top of the tip13 of the main magnetic pole 11 (top of the main magnetic pole 11 in themiddle of the manufacturing process). After the resist 23 thus providedis flattened as necessary, a dielectric layer or metal layer 24 isformed on the resist as shown in FIG. 2A. The dielectric or metal layer24 may be formed from any material which can be selectively etched awayalong with the resist.

[0111] Then, a hole 25 is patterned on a portion of the dielectric ormetal layer 24 below which the electron emitter 40 is to be formed, asshown in FIG. 2B. The hole 25 may be circular or square in shape.However, the length of the hole 25 in the direction of track widthshould be defined such that the top end width of the recording trackgenerally coincides with the recording track width. The hole length inthe direction of the track should be defined to be such a one that theelectron emitter 40 can be sharpened or tapered at the top thereof aswill further be described later.

[0112] On the assumption that the track width is Tw and height of theelectron emitter 40 to be formed is He, the length of the hole in thedirection of the track width should desirably be on the order of Tw+2nHe(where n is a parameter depending upon the distribution of the angle ofinjection of a material into the hole 25 when forming the electronemitter 40 in the hole 25) and that of the hole in the direction of thetrack should also desirably be about 2nHe for such a sharp or taperedtop end portion of the electron emitter 40 as will enable an efficientfield emission. When the material is injected at an angle nearer to thenormal line, the parameter n is smaller. When the material is injectedat an angle further from the normal line (more isotropically), thparameter n is larger. When n=1, the taper angle of the electron emitteris 45°. That is to say, the size of the hole 25 depends upon the trackwidth Tw as well as upon both the parameter n depending upon the methodof forming the electron emitter 40 and height of the electron emitter40.

[0113] More specifically, the recording track width Tw (track width ofthe tip 13 of the main magnetic pole 11) is selected to be 0.75 μm, theheight He of the electron emitter 40 is 0.25 μm, the size of the hole 25is 1.25 m in the direction of the track width and 0.5 μm in thedirection of the track (n=1), for example, in the present invention. Thehole 25 may be formed by either the PEP or FIB process.

[0114] Thereafter, the resist 23 is etched by wet etching through thehole 25 to form a cavity 26 in which the electron emitter 40 is to beformed, as shown in FIG. 2C. Next, the material for the electron emitter40 is injected into the cavity 26 by evaporation or sputtering fromabove the hole 25. The material for the electron emitter 40 may be ahigh melting point metal such as Mo, W, Ta or the like, a semiconductorsuch as Si, Ge or the like, or carbon (C). Among these materials, thecarbon (C) is suitably usable to assure a stable service and long lifeof the electron emitter used in the atmosphere.

[0115] By injecting the material for the electron emitter 40 onto theelectrode layer 30 in the cavity 26 from above the hole 25, an island ofthe electron emitter material is initially formed on the electrode layer30. The island has a size nearly same as that of the hole 25. Thematerial for the electron emitter 40 is heaped on the electrode layer 30while being heaped as indicated with reference numeral 42 on thedielectric or metal layer 24. The adhesion of the layer 42 to the wallof the hole 25 is defined by the distribution of the angle of injectionof the electron emitter material into the hole 25, and the distributioncan be controlled.

[0116] For example, when sputtering method is employed, the distributionof the angle of injection can be controlled based on the distancebetween a sputtering target and hole 25 and sputter gas pressure or theaspect ratio of a through-hole formed between the sputtering target andhole 25. When the direction of the injection into the hole 25 is nearerto the normal line with respect to the electrode layer 30, the taperangle of the electron emitter 30 (angle from the electrode layer 30) islarger, namely, the electron emitter 40 is tapered more sharply. On theother hand, when the direction of the injection is more isotropic, theelectron emitter 40 is tapered more gently.

[0117] It is essential to limit the radius of curvature of the top endportion of the electron emitter 40 to about 10 nm and make the height ofthe top end nearly coincide with that of the top of the recordingmagnetic pole (main magnetic pole) 11. These radius of curvature andheight of the top end can be controlled buy adjusting the thickness ofthe resist layer 23, thickness of dielectric or metal layer 24, size ofthe hole 25 and method for heaping the electron emitter material. At thebeginning of the material for the electron emitter 40 being thus heaped,it has the same size as the hole 25 when it is still near the electrodelayer 30. The material is further heaped on the wall of the hole 25 aswell as on the electrode layer 30. The material 42 will further beheaped on the wall of the hole 25 so that the hole 25 will be narrowerat it goes upward. Namely, the effective size of the hole 25 will bereduced because the space in the hole 25 is reversely tapered.

[0118]FIG. 2D shows the shape the electron emitter 40 will be formed tohave in the course of the material being heaped.

[0119] As the electron emitter material further grows as in the above,the top end portion of the electron emitter 40 will be graduallytapered. When the layer 42 of the same material as for the electronemitter 40, heaped on the dielectric or metal layer 24, has grown untilit closes the hole 25, the electron emitter 40 will have a sharp taperedshape as shown in FIG. 2E. By observing the shape of the electronemitter thus formed by an electron microscope, it was confirmed that thetaper angle formed between the lateral sides of the electron emitter 40was about 45°, namely, the tapered portion being a ridge longer in thedirection of the track width while being shorter in the direction of thetrack, the track width at the top end portion of the electron emitter 40is nearly 0.75 μm and the curvature of the top end portion is nearly 10nm.

[0120] By removing the dielectric or metal layer 24 and resist 23 at thefinal step, a thermally-assisted magnetic recording head as shown inFIGS. 1A and 1B can be provided. No read element is shown in FIGS. 1Aand 1B, but a read element may be formed at either the leading side ortrailing side of the write element, for example, as in an ordinaryplanar type magnetic head.

[0121] Referring now to FIG. 3, there is shown an embodiment of the readelement which may be disposed at the leading or trailing side in FIGS.1A and 1B. In FIG. 3, the reference S indicates a head substrate, X amedium moving direction (at the trailing side), 7 an adjusting layer, 8an electrode, 9 a yoke, 91 a yoke end, 10 a GMR (giant magentoresistive)element, 11 an insulator, 60 a medium, 61 a recording layer and 62 alining layer. In the above construction, the adjusting layer 7 is notalways necessary. Note that in FIG. 3, the elements having the same orsimilar functions as or to those of the elements shown in FIGS. 1Athrough FIG. 2E will be indicated with the same or similar referencenumerals as those in FIGS. 1A through 2E. They will not be described indetail.

[0122] The read element shown as an example in FIG. 3 can bemanufactured in parallel to the aforementioned write element as in thefollowing. The adjusting layer 7 is formed on an ALTIC substrate to makethe top of the yoke end 91 generally coincide with that of the tip 13 ofthe main magnetic pole 11. Next, a resist frame is formed on theadjusting layer 7 to form the Cu electrode 8 for example. After removingthe resist, the insulator 11 of SiO₂ for example is buried up to thebottom of the GMR element 10, and then it is tapered by etching toexpose the electrode 8. The yoke 9 is formed by frame plating of the GMRelement 10 down to the bottom of the latter. After the yoke 9 isflattened as necessary, the GMR element 10 is formed before patterning.The GMR element 10 may be formed from a lamination of Co, Cu, Co andFeMn layers.

[0123] Next, the portion of the insulator 11, over the GMR element 10,is formed and tapered by etching to expose the lower portion of the yoke9. Then, the upper portion of the yoke 9 is formed by frame plating. Theyoke end 91 and read gap (between two ends) have to be fine-worked. TheFIB process is used to work them as necessary to form a pattern ofseveral tens of nm. The yoke end 91 is provided to pick up signalmagnetic field depending upon the magnetized direction of the recordinglayer 61 of the medium 60, and the picked-up signal is read by the GMRelement 10 buried in the insulator 11.

[0124] A substrate having provided thereon the magnetic recordingelement in FIGS. 1A and 1B, provided with the electron emitter 40produced as in the above, and the read element in FIG. 3, disposed atthe trailing side in FIGS. 1A and 1B, is cut into stripes, and eachstripe is cut into chips, each chip is worked into a slider, then theslider is mounted on a suspension to provide a thermally-assistedmagnetic recording head according to the present invention. Note thatthe thermally-assisted magnetic recording head according to the presentinvention can also be produced by attaching a thin film element onto anappropriate substrate other than the ALTIC substrate, coating it with aprotective member, separating the thin film element from the substrate,attaching it on a slider, and finishing the surface.

[0125] In embodying the present invention, the field intensity at thetip of the electron emitter is important, so when the magnetic recordinghead levitates, a variation of the head levitation will undesirably leadto a variation of the field intensity. To avoid this, the slider shouldbe designed to a contact pad type which is slidable in contact with themedium. When the slider moves in contact with the medium, the headlevitation will not vary but the load acting on between the head andmedium will vary. There is coated on the sliding surface of the head onthe medium a DLC (diamond-like carbon) layer of about 5 nm in thicknessto protect the head.

[0126] Next, an embodiment of the medium installable in thethermally-assisted magnetic recording device according to the presentinvention will be described. The basic construction of the medium is asshown in FIGS. 1A and 1B. No medium-protective layer and lubricant areillustrated in FIGS. 1A and 1B for the simplicity of illustration.Normally, however, they should desirably be provided. This embodiment ofthe medium can use a vertically magnetizable, multiparticle layer with asoft-magnetic base layer. More specifically, a soft-magnetic base layer62 of NiFe is formed to a thickness of 100 nm on a glass substrate, thena vertically magnetizable, multiparticle layer 61 of CoPt and SiO₂films, is formed to a thickness of 20 nm on the base layer 62, and aprotective layer of C is formed to a thickness of 3 nm on the layer 61,all by sputtering. Further, a lubricant is coated on the protectivelayer and the surface irregularities are removed by tape burnishing. Inthis embodiment, the recording layer 61 is made of a so-called granularlayer having a structure in which magnetic particles of CoPt aredispersed in a base material of SiO₂. This is because the size andcontent of the magnetic particles can easily be controlled. For formingthe recording layer 61 of CoPt and SiO₂ films, binary sputtering is madewith a CoPt target and SiO₂ target, and the particle size and CoPtcontent are controlled by varying the sputter input to each of thetargets. Also, only the particle size may be controlled independently bythe bias power by applying a bias to the substrate during sputtering.

[0127] Before conducting experiments on the write and read by thethermally-assisted magnetic recording head according to the presentinvention, the composition, fine structure and magnetic characteristicof the medium involved in the present invention were examined. Thecontent of CoPt in the CoPt—SiO₂ layer formed under the typicalconditions was 60% by volume. The result of the fine structure analysisproved that the CoPt and SiO₂ particles are separate from each other andthe SiO₂ base material was spotted with the CoPt particles. The meansize of the CoPt particles was about 7 nm. The magnetic characteristicwas measured as will be described below. Namely, a torque meter and VSMwere used to examine the thermal characteristic at differenttemperatures included in a range of liquid nitrogen temperature to 500°C. The typical magnetic characteristics measured at the room temperaturewere: Ku: 4.5×10⁶ erg/cc, Hc: 5 kOe, and Ms: 400 emu/cc. The particleshaving the mean size was found to have a KuV/kT value of about 125 atthe room temperature (300 K). Thus, the medium used in this embodimentcan be said to show an ambient thermal agitation at a temperature nearthe room temperature. The magnetic characteristic varied as a functionof the temperature and was found to be monotonously lower in a directionfrom a low temperature to a high temperature.

[0128] Referring now to FIG. 4, there is illustrated a graph of thedependence on the temperature of Hc measured using VSM and that of Hc0estimated using the Sharrock's expression. Since VSM takes a time ofabout 10 minutes for loop measurement, Hc measured by VSM is a coerciveforce after the magnetic field is subjected to a thermal agitation forabout 10 minutes at the temperature. On the other hand, the coerciveforce Hc0 associated with the recording is a magnetic field required fora high speed magnetic transition for about 10 ns during actual recordingby the head. It means a magnetic field required for a magnetictransition within a time for which it will be little influenced by athermal agitation. In a temperature range in which the magnetic fieldwill be little affected by the thermal agitation within a time of about10 minutes, Hc and Hc0 will nearly (completely when K is zero) coincidewith each other, but in a high temperature range, Hc will beconsiderably lower than Hc0. Important in the thermally-assistedmagnetic recording is not Hc but Hc0. So, Hc0 was determined based on acombination of the measurement with VSM and Sharrock's expression.

[0129] As the result, Hc0 measured at a temperature near the roomtemperature was 5.2 kOe which is nearly the same as Hc, but in atemperature range higher than 100° C. equivalent to the temperatureduring the thermally-assisted recording, Hc was considerably higher thanHc0. The saturation magnetic field of the medium required for therecording should preferably be nearly double Hc0. However, since thesaturation field is nearly proportional to Hc0, the present inventionwill be described below using Hc0 as the necessary magnetic field forthe thermally-assisted magnetic recording. Note that when K is zero, theanisotropic energy Ku0 was 8×10⁶ erg/cc and saturation magnetization Ms0was 600 emu/cc. Since the CoPt content in the layer was 60% by volume,the net magnetization Isb was 1000 emu/cc. When the hightemperature-side Hc0 was extrapolated, the Curie point was estimated tobe five hundreds and several tens of ° C. and the temperature at whichHc0 decreased to 2 kOe was estimated to be about 300° C.

[0130] In the experiments, the medium having the above-mentionedmagnetic characteristic was set along with the thermally-assistedmagnetic recording head in a spin-stand type magneticrecording/reproducing evaluation apparatus, the medium was moved at arate of 10 m/s in relation to the head, and the write and read weretested with a relatively low linear density equivalent to a solitarywave output of 100 kfci to examine the read output voltage. The head wasmoved in contact with the slider, the spacing was controlled in a rangeof 8 to 10 nm, that is, a range from a sum (8 nm) of the head protectivelayer thickness and medium protective layer thickness to a sum (10 nm)of the lubricant layer thickness and the sum of the layer thickness. Asvariables of write and read, the emission electron current was varied bychanging the voltage applied to the electron emitter and the recordingfield intensity was varied by changing the current supplied to therecording coil 21. The electrode 30 of the electron emitter 40 wasapplied with a voltage being negative in relation to the groundpotential, and the medium was at the ground potential. The voltageapplied to the electron emitter 40 may be either a DC or pulse voltage.

[0131] Referring now to FIG. 5, there is graphically illustrated arelation between a voltage Ve applied to the electron emitter and GMRread output voltage Vs per 1 μm of track width in which a current Iwsupplied to the recording coil 21 is taken as parameter. In FIG. 5, onlytwo examples, Iw of 20 mA and Iw of 40 mA, are shown. However, when theapplied voltage Ve was lower than 7.5 V, no read output could beprovided with the supplied current Iw increased to a largest possibleone. On the contrary, when a voltage Ve applied to the electron emitterwas higher than 15 V with the current Iw supplied to the recording coil21 being 40 mA which is a practical value for use in the magnetic discdrive, and more preferably when the applied voltage Ve was higher thanabout 25 V with the supplied current Iw being 20 mA, a high saturationread output could be provided, which proves that the present inventionis highly advantageous.

[0132] Further, some thermally-assisted magnetic recording heads wereexperimentally prepared by varying a track-directional distance Dbetween the top end portion of the electron emitter 40 and the leadingedge of the tip 13 of the main magnetic pole has in FIGS. 1A and 1B andwere similarly tested. The test result proved that if the distance D istoo long, the medium once heated by the electron beam would be coldbefore the magnetic field-applied portion thereof was reached, so thatno significant recording was possible. The range of the distance D whichenables the significant recording was found to be 500 nm or less,preferably, 250 nm or less, and most preferably, 100 nm or less. Thetest result shown in FIG. 5 corresponds to the test with the distance Dof 250 nm. As seen from FIG. 5, the shorter he distance D, the lower thevalues Ve and Iw necessary for the saturation recording were. However,even when the distance D was set as short as possible, no significantrecording was possible with the applied voltage Ve being 5 V or less. Aswill further be described later, in case of a head having a ridge whoseline is directed towards the track, a significant recording is possibleeven with the distance D being longer than the above.

[0133] Next, the recording mechanism of the thermally-assisted magneticrecording device according to the present invention will be describedherebelow with reference to FIGS. 6A through 6C.

[0134]FIGS. 6A through 6C schematically shows the process of recordingby the thermally-assisted magnetic recording head according to thepresent invention. FIG. 6A is a sectional view of an portion extractedfrom FIG. 1B and associated with the recording process, FIG. 6Bgraphically shows an electron beam profile on the medium and atemperature distribution on the medium and FIG. 6C graphically shows aspatial distribution of the medium coercive force and that of therecording magnetic field. In FIG. 6A, reference numeral 11 indicates amain magnetic pole, 13 a tip of the main magnetic pole, 17 a magneticflux generated by the main magnetic pole 11, 30 an electron emitterelectrode, 40 an electron emitter, 41 an electron beam, 60 a medium, 61a recording layer, 62 a soft-magnetic lining layer, 63 a medium heater,64 a magnetically recording portion of the medium 60, and 65 amagnetization of the medium 60. In FIG. 6A, the elements having the sameor similar functions as or to those of the elements shown in FIGs. 1Aand 1B will be indicated with the same or similar reference numerals asthose in FIGS. 1A and 1B. They will not be described in detail.

[0135] In FIG. 6A, the reference Ve indicates a voltage applied to theelectron emitter 40, D a track-directional distance between the top endportion of the electron emitter 40 and leading edge of the tip 13 of themain or recording magnetic pole 11, X a moving direction of the medium60, Be an electron beam profile on the medium surface, Tm a mediumtemperature, Hc0 a coercive force of the medium 60, and Hw a recordingmagnetic field.

[0136] The medium 60 is moved from left to right (in the plane of FIG.6A; the left side of the plane is leading side while the right side istrailing side) in relation to the head, and a voltage Ve is applied tothe electron emitter 40 to direct an electron beam 41 from the top endportion of the electron emitter 40 towards the recording layer 61. Thespatial distribution of the electron beam incident upon the medium 60 isas indicated with Be in FIG. 6B. The recording layer 61 is heated by theelectron beam 41 having the profile Be. Since the medium 60 is moved ata high speed, the temperature of the recording layer 61 will delineate acurve whose peak is shifted towards the trailing side in relation to theelectron beam profile Be, that is, a curve Tm in FIG. 6B. Thedistribution of the coercive force Hc0 of the medium 60 depends upon thetemperature distribution Tm and temperature characteristic of Hc0 shownin FIG. 4 and delineates a curve Hc0 shown in FIG. 6C. The distributionof Hc0 and distribution Hw of a magnetic flux 18 generated by therecording magnetic pole 11 and interlinking the medium 60 intersect eachother at a position 64 the magnetized direction of the medium 60 dependson.

[0137] As seen from FIG. 6C, the trough of Hc0 is deeper as the power orenergy of the incident electron beam is higher, while the crest of Hw ishigher as the current Iw supplied to the recording coil 21 is larger.The position where Hc0 and Hw curves intersect each other shiftsdepending upon the distance D between the top end portion of theelectron emitter 40 and leading edge of the tip 13 of the recordingmagnetic pole 11.

[0138] As seen from FIG. 6C, the magnetic transition point in thethermally-assisted magnetic recording according to the present inventiondiffers from that in the conventional magnetic recording and will alsolie at other than the trailing edge of the tip 13 of the recordingmagnetic pole 11.

[0139] In the conventional magnetic recording not thermally assisted,since Hc0 of the medium 60 is spatially uniform and a larger recordingmagnetic field than Hc0 is applied to provide a magnetic transition, themagnetic transition position necessarily lies in the trailing edge ofthe tip 13 of the recording magnetic pole 11. On the contrary, in thethermally-assisted magnetic recording according to the presentinvention, the magnetized direction coincides with the direction of therecording magnetic field only within an area defined between Hc0 and Hwcurves intersecting at two points. When the direction of the recordingmagnetic field is reversed at a time when the medium 60 passes bybetween Hc0 and Hw, a magnetic transition takes place at that position,therefore, the magnetic transition will not always take place in thetrailing edge of the recording magnetic pole 11 but in an arbitrary areabetween Hc0 and Hw curves intersecting at two points and between theleading and trailing edges.

[0140] In FIG. 6A, there are shown only the major components of therecording device and medium in the form of a lateral sectional view.However, it should be noted that when the intensity distribution of theelectron beam on the medium surface is curved in the direction of thetrack width, the line between the points of intersection between Hc0 andHw curves. Therefore, the magnetic transition provided by thethermally-assisted magnetic recording according to the present inventionis curved in the direction of the track width as the case may be. Thedevelopment of the magnetic transition not always only in the trailingedge of the tip of the recording magnetic pole 11 but also at anarbitrary point between the points of intersection between Hc0 and Hwcurves and occasional curving of the magnetic transition in thedirection of the track width can be counted at the differences of thethermally-assisted magnetic recording according to the present inventionfrom the conventional magnetic recording.

[0141] In the foregoing, the first or basic embodiment of the presentinvention has been described in which a low recording frequency isselected for the purpose of definite examination of the behavior of thesignal output. However, it is of course that the present invention canrealize a quality thermally-assisted magnetic recording even with a highlinear density.

Second Embodiment

[0142] Next, the present invention will be described herebelowconcerning its second embodiment of the thermally-assisted magneticrecording device.

[0143] In the first embodiment of the thermally-assisted magneticrecording device according to the present invention, the multiparticlelayer was used as the medium. The present invention is advantageous whenthe medium is formed from a continuously magnetic layer, that is, anamorphous magnetic layer, too. A medium formed from a layer of aferrimagnetic alloy of an amorphous rare earth and transition metal (R-Tlayer) and used as a magneto-optical recording medium, wasexperimentally prepared and installed in the thermally-assisted magneticrecording device according to the present invention. The secondembodiment was evaluated similarly to the first embodiment having beendescribed in the foregoing.

[0144] The medium is constructed by forming on a glass substrate a heatsink layer of an Al alloy, TbFeCo recording layer of TbFeCo, protectivelayer of C and a lubricant layer in this order. The heat sink layer wasprovided to adjust the thermal response of the recording layer.

[0145] Referring now to FIG. 7, there is graphically illustrated athermally-assisted magnetic characteristic of the medium experimentallyprepared. In FIG. 7, Hc is a coercive force and Ms is a saturationmagnetization related to a read signal. In a continuously magnetic layersuch as a magneto-optical layer, since no thermal agitation will takeplace, Hc and Hc0 basically coincide with each other in the entiretemperature range. In this second embodiment, the composition of therecording layer was adjusted so that Ms at a temperature near the roomtemperature was 200 cmu/cc or so for an ample magnetic signal. Also, thecompensation point was set to about 100° C., recording point to twohundreds and several tens of ° C., and the Curie point was to 300° C.The medium was set along with the thermally-assisted magnetic recordinghead according to the present invention in the spin-stand typeevaluation apparatus and subject to the same evaluation as for the firstembodiment. The evaluation result was almost same as that of the firstembodiment.

[0146]FIG. 8 graphically explains the concept of information recordingto the medium in FIG. 7 according to the present invention. Theconstruction of the thermally-assisted magnetic recording head,intensity distribution of the electron beam, and temperaturedistribution on the medium are exactly as shown in FIG. 6B. Differentfrom in FIG. 6B is the Hc distribution on the medium. Since thecompensation point is set to nearly 100° C., Hc will be distributed asshown in FIG. 8 correspondingly to a temperature distribution Tm to thatshown in FIG. 6B. The Hc curve and curve of the magnetic field Hwapplied by the recording medium will intersect each other at a positionthe magnetized direction depends on.

Third Embodiment

[0147] Next, the present invention will be described herebelowconcerning the third embodiment thereof.

[0148] According to this embodiment, the thermally-assisted magneticrecording head according to the present invention was produced with somedifferent settings of the track width Tc of the top end portion of theelectron emitter and track width Tw of the tip of the recording magneticpole, respectively, as shown in FIGS. 1A and 1B or FIG. 6A. The head wascombined with the medium included in the first embodiment, and evaluatedsimilarly to the first embodiment, and also the cross-erase (erasure ofrecord signal on an adjacent track) was evaluated.

[0149] In the third embodiment, the track width of the tip of therecording magnetic pole was fixed to 0.75 μm, the length in thedirection of the track width of the hole (25 in FIGS. 2B and 2C) forforming the electron emitter was changed, and the track width Te of thetop end portion of the electron emitter was changed. Also, the trackpitch was set to 1 μm, recording was made to five tracks adjacent toeach other with different recording frequencies, and then recording tothe middle track was repeated 105 times to examine whether the recordsignal in the adjacent tracks would be deteriorated.

[0150]FIG. 9 graphically shows the result of the evaluation of the thirdembodiment of the present invention. In the graph, the horizontal axisshows Te/Tw ratio while the vertical axis shows read output. Thereference A indicates a read output from the track, recorded as in thefirst embodiment, and B indicates a read output from a track adjacent tothe track to which recording was repeatedly made 105 times (the readdata had been pre-recorded with a difference frequency from that for thetrack to which 105 times of recording was repeated). The curve A willmake it clear that the read output falls suddenly with the Te/Tw ratiobeing of less than 1/2. This is because with a too small a Te/Tw ratio,it is difficult to sufficiently heat the medium over the track width andno significant recording is possible near the track edge.

[0151] Also it will be known from the curve B that with two large aTe/Tw ratio, signals already recorded in tracks adjacent to the one towhich recording was repeatedly made are deteriorated. It is consideredas the reason for the above that although no recording magnetic fieldwill be applied to any adjacent tracks during recording, too large aTe/Tw ratio will cause the end portions of the adjacent tracks to heatedand data to be gradually destroyed by thermal agitation. As seen fromFIG. 9, it is preferable in this embodiment of the present invention toestablish a relation of 1/2 Te≦Tw≦2Te between the track width Te of theelectron emitter and track width Tw of the tip of the recording magneticpole.

Fourth Embodiment

[0152] Next, the present invention will be described herebelowconcerning the fourth embodiment thereof.

[0153] The fourth embodiment is a thermally-assisted magnetic recordinghead having a plurality of electron emitters provided in the directionof the track.

[0154] Referring now to FIG. 10, there are illustrated in the form of asectional view essential components of the thermally-assisted magneticrecording head, by way of example, having a plurality of electronemitters provided therein. In FIG. 10, reference numeral 11 indicates amain magnetic pole, 13 a tip of the main magnetic pole 11, 30 anelectron emission electrode, 401 is a first electron emitter, 402 asecond electron emitter, and 403 a third electron emitter. In FIG. 10,the elements having the same or similar functions as or to those of theelements shown in FIGS. 1A and 1B or FIG. 6A will be indicated with thesame or similar reference numerals as those in FIGS. 1A and 1B or 6A.They will not be described in detail. FIG. 10 illustrates an embodimentin which three electron emitters are provided. However, the presentinvention is not limited to this number of electron emitters but can usemore than three electron emitters. This embodiment is speciallyadvantageous in that the efficient of medium heating is improved byproviding the plurality of electron emitters in the direction of thetrack. Any electron emitters disposed too far from the recordingmagnetic pole will not work so effectively. The preferable number of theelectron emitters used in the present invention is two to five in total.

[0155] The plurality of electron emitters shown, by way of example, inFIG. 10 can be formed by somewhat modifying the manufacturing processfor the first embodiment, having previously been described withreference to FIGS. 2A THROUGH 2E. Namely, in the process in which thehole is formed in the dielectric or metal layer 24, shown in FIG. 2B, itsuffices to form a plurality of holes of a predetermined size in thedirection of the track. When the plurality of electron emitters isprovided, the distance between the top end portions thereof shouldpreferably be short. Therefore, to form the electron emitters 401 to 403(as in FIG. 2D), a highly anisotropic method such as the long-slowsputtering, collimated sputtering or the like should be adopted, and theheight of the electron emitters should be low.

[0156] The thermally-assisted magnetic recording head provided with theplurality of electron emitters thus formed was evaluated similarly tothe first embodiment. As the evaluation result of the first embodiment,the range of the distance D enabling significant recording was proved tobe 500 nm or less, preferably 250 nm or less, and more preferably 100 nmor less. The evaluation result of the fourth embodiment proved thatsufficiently significant recording was possible with a distance D beingmore than double that in the first embodiment. In the evaluation of thefourth embodiment, an integration in the direction of the track of theheat developed by the electron beams emitted from the individualelectron emitters was taken as the medium temperature. The distancebetween the electron emitters should be equal to the distance D whichshould be when the single electron emitter is used.

[0157] On the other hand, the same effect can also be assured bychanging the direction of the ridge of the electron emitter instead ofproviding the plurality of electron emitters. More specifically, theelectron emitter in FIGS. 1A and 1B should be formed rectangular in thedirection of the track (it should be turned 90° in the plane of FIG.1B). Also in this case, the electron incident area of the medium will belonger in the direction of the track, so that the medium can be heatedwith a high efficiency. The track width in this case may be defined tobe a one which would be when the plurality of electron emitters isprovided in the direction of the tack width, or several tens of nm whichwould be defined when the single electron emitter is provided. Note thata top end portion of 10 nm or so of the electron emitter can effectivelyemit electrons as having previously been described. However, by applyinga higher electric field, the effective electron emitting portion can beextended to 20 nm or so. Also, since the electric field distributionbetween the top end of the electron emitter and medium surface has aprofile extending somehow on the medium surface, the electron incidentarea of the medium surface is wider than the electron emitting area. Forexample, when the spacing is 10 nm or so, the electron incident areawill be 20 to 30% wider than the electron emitting area. With thespacing being small, the electron emitting area and electron incidentarea will be equal in size to each other.

Fifth Embodiment

[0158] The aforementioned embodiments are combinations of a planar typemagnetic recording had and electron emitter. However, the presentinvention is applicable to a laminated type thin magnetic head.

[0159] Referring now to FIG. 11, there is illustrated in the form of asectional view a thermally-assisted magnetic recording head composed ofa laminated type thin magnetic head and electron emitter according tothe present invention. In FIG. 11, reference numeral 11 indicates a mainmagnetic pole, 12 a return-path magnetic pole, 13 a tip of the mainmagnetic pole 11, 14 a connection between the main magnetic pole 11 andreturn-path magnetic pole 12, 21 a coil, 22 a layer in which the coil 21is buried, 30 an electrode, 32 a read gap, 31 an insulative layer, 33 anupper shield, 10 a GMR read element, 60 a medium, 61 a recording layer,62 a lining layer, S a substrate, and X a medium moving direction. InFIG. 11, the elements having the same or similar functions as or tothose of the elements shown in FIGS. 1A and 1G or FIG. 3 will beindicated with the same or similar reference numerals as those in FIGS.1A and 1B or FIG. 3. They will not be described in detail.

[0160] The thermally-assisted magnetic recording head shown, by way ofexample, in FIG. 11 can be produced following the procedure given belowfor example. The substrate S should desirably be an ALTIC substrateeasily workable into a slider. The electrode 30 for the electron emitteris provided in the form of a stripe on an insulative layer formed, ifapplicable, on the substrate S or directly on the substrate S. A layerof carbon (C) is provided also in the form of a stripe on the electrode30. After the lamination thus formed is flattened, an insulative layer31 is formed thereon, and the main magnetic pole 11 is formed by frameplating. The top end portion of the main magnetic pole 11 is etched toform the tip 13.

[0161] Next, the coil 21 of Cu is formed by frame-etching and athrough-hole is formed in the connection 14. Then, the connection 14 isformed by frame plating, and also the return-path magnetic pole 12 isformed by frame plating. The surface of the return-path magnetic pole 12is flattened.

[0162] Further, the read gap layer 32 is formed to a half or so thereof,the GMR element is formed, and a hard bias layer and Cu lead are formedat opposite sides of the GMR element. Thereafter, the rest of the readgap layer 33 is formed and then the upper shield 33 is formed. In thisstate, the top end portion of the electron emitter has no ridge yet butit has the shape of a square pole. After the thin layers are thus formedon the substrate S, the substrate S is cut into stripes and each stripeis cut into chips, and thus the surface of an ABS layer is exposed. Aprotective layer is coated on the ABS surface, and finally FIB processis used to taper the top end portion of the electron emitter (made of C)from both sides thereof. At this time, the tip 13 of the main orrecording magnetic pole 11 may be trimmed as necessary.

[0163] The thermally-assisted magnetic recording head thus constructedfollowing the above procedure was evaluated similarly to theaforementioned embodiments. The evaluation result proved the effect ofthe present invention as with the aforementioned embodiments.

Sixth Embodiment

[0164] Next, the present invention will further be described concerningthe sixth embodiment thereof with reference to FIG. 12.

[0165] This embodiment relates to a system configuration of thethermally-assisted magnetic recording device.

[0166]FIG. 12 is a block diagram of the thermally-assisted magneticrecording device according to the present invention, showing an exampleof the system construction of the recording device. In FIG. 12, thereference Ie indicates an electron emitter drive input, Is a signalinput, Os is a signal output, 101 an electron emitter drive circuit, 102an electron emitting element incorporated in the head, 103 an ECC (errorcorrection code) append circuit, 104 a modulation circuit, 105 a recordcorrection circuit, 106 a write element incorporated in the head, 107 amedium, 108 a read element incorporated in the head, 109 an equivalentcircuit, 110 a demodulation circuit, 111 a demodulation circuit, and 112an ECC circuit.

[0167] Different from the conventional magnetic disc drive not of thethermally-assisted type, this embodiment is characterized by theaddition of the electron emitter drive input Ie, electron emittingelement drive circuit 101 and electron emitting element 102, the novelhead construction as having previously been described concerning theaforementioned embodiments, and the specially adjustedthermally-assisted magnetic characteristic of the medium as havingpreviously been described concerning the aforementioned embodiments.

[0168] To drive the electron emitter, a DC voltage may be applied to theelectron emitter or the electron emitting element may be DC-driven withno electron emitting element drive circuit being provided. Also, theelectron emitter may be driven in a pulsed manner synchronously with anoutput from the modulation circuit 104. The pulsed drive will make morecomplicate the circuit configuration, but it is preferable for a longerservice life of the electron emitter. The ECC append circuit 103 and ECCcircuit 112 may not be provided. The modulation and demodulation method,and record correcting method may freely be selected.

[0169] Information is read to the medium by directing an electron beamfrom the electron emitting element 102 to the medium and applying arecording magnetic field derived by modulating a recording signal fromthe write element 106 to a position on the medium where Hc0 has beenlowered due to the incident electron beam. Forming of information to bewritten as a magnetic transition train on the medium surface is the sameas in the conventional magnetic recording device. However, when theelectron beam is curved in the direction of the track idth, the magnetictransition is also curved in the direction of the track width. Afringing field developed from the magnetic transition train and comingfrom the medium is detected as a signal field by the read element 108.

[0170] The read element 108 is typically of GMR type, but it may be ofthe ordinary AMR (anisotropic magnetoresistance) type. It may be of aTMR (tunneling magnetoresistance) type in future.

[0171] The thermally-assisted magnetic write and read by thethermally-assisted magnetic recording device according to the presentinvention were evaluated. The result is equal to that obtained by theevaluation of the aforementioned embodiments using the spin-stand typeevaluation apparatus.

Seventh Embodiment

[0172] Next, the present invention will further be described concerningthe seventh embodiment thereof with reference to FIG. 13.

[0173] This embodiment provides a thermally-assisted magnetic recordingdevice in which the atmosphere around the electron emitter is controlledto further improve the reliability.

[0174] Before proceeding to the description of the seventh embodiment ofthermally-assisted magnetic recording device according to the presentinvention, the experiments the Inventors of the present inventionconducted and the experiment results will be described in detailherebelow. In the process to work out this embodiment, the Inventorsmade experiments on how the atmosphere around the electron emittershould be.

[0175]FIG. 13 is a block diagram of the apparatus used in theexperiments conducted by the Inventors of the present invention. Theapparatus shown in FIG. 13 is a modified one of STM (scanning tunnelingmicroscopy). The modifications of STM will mainly be described below.

[0176] First modification: Carbon (C), Ta (tantalum) and Si (silicon)were coated on the layer of Pt (platinum) normally used to form theprobe (corresponding to the electron emitter in the present invention)in STM to provide a probe made of materials generally used to form thefield emission emitter.

[0177] Second modification:

[0178] A sample having a dummy medium surface formed by coating a C(carbon) layer on a glass substrate was prepared as an object to bemicroscoped by STM (corresponding to the recording medium according tothe present invention).

[0179] Third modification: This is related to the control of a distancebetween the probe and sample. In ordinary STM, the probe tip and samplesurface are disposed several A (angstrom) off each other so that atunnel current will flow. To detect a field emission current flowingover a distance of 10 nm or so, the Inventors of the present inventioncontrolled an inchworm element by a sample holding circuit to move thesample in relation to the probe in a pulsed manner at a rate of 4nm/step so that the distance between the probe and sample surface couldbe fixed to 10 nm or so.

[0180] Fourth modification: This is related to an increase of the rangeof measuring current. In ordinary STM, a tunnel current of 0.3 to 0.5 mAis used. However, since a field emission current of 10⁻⁴ A isadvantageously used in the thermally-assisted magnetic recording deviceaccording to the present invention, the I-V amplifier was modified for avariable IV-converted resistance to monitor a current of 10⁻⁴ A or so.Furthermore, a modification was made so that when an emission current of10⁻⁴ A or so was detected, a control in a constant current mode wasstarted to enable measurement of a time for which the current continuedto flow stable. The voltage applied to the probe was made variablebetween 0 and 15 V. Also, the probe and sample were disposed in a sealedcontainer in which the internal atmosphere could freely be changed.

[0181] Using the experimental apparatus constructed as in the above, theexperiments on this embodiment were conducted following the proceduregiven below:

[0182] First, with the probe kept at the ground potential, the probe wasmoved towards the sample surface to detect a tunnel current. It can beestimated that at this time, the probe and sample surface were several A(angstrom) off each other. The inchworm was driven taking this distanceas a reference to move the sample from the probe at 2 to 3 steps, andthe sample was fixed by the sample holding circuit. While applying avoltage gradually to the probe and varying the IV-converted resistanceof the I-V in this condition, the field emission current was measured ina wide range of the current.

[0183] The probe used was a Pt probe normally used in ordinary STM andhaving C, Ta and Si coated to a thickness of about 2 to 5 nm by sputtercoating. The atmosphere inside the container in which the probe wasplaced was changed to various degrees using a evacuation pump and gasinlet system. The composition of the gas in the sealed container wasanalyzed wit a quadrupole mass spectrometer (QMS) mounted on thecontainer. When the internal pressure of the container was higher thanthe operating pressure of QMS, the gas was sampled through an orifice.The diameter of the orifice was varied depending upon the internalpressure of the container so that measurement was always possible with ahigh sensitivity. The output of QMS was calibrated with an output whichwas when an object gas (mainly oxygen) was introduced in 100% at apredetermined pressure to determine an absolute value of the partialpressure of the gas. Also, the experiment was conducted in a clean roomso that the number of particles inside the container would be less thanClass 100. After replacing the probe and sample, the container insidewas cleaned back to a predetermined atmosphere by purging a dry nitrogenseveral times.

[0184]FIG. 14 graphically shows a relation between a field emissioncurrent I and voltage V applied to a probe, experienced using two probesmade of Ta (tantalum) and C (carbon), respectively, in a depressurizedatmosphere of 10×10⁻⁴ Pa. Since the distance between the top end of theprobe and sample surface is fixed to 10 nm as having previously beendescribed, the voltage of 1 V is equivalent to a field intensity of 10⁶V/cm. The behavior of the emission current against the field intensitywas such that the Ta probe having a shape reflecting the Fowler-Nordheimexpression and having a low work function provided a larger emissioncurrent than the C probe having a higher work function. Namely, theexperiment results provide reasonable data. The Inventors conducted asimilar experiment on a probe made of Si. The emission current of thisprobe was an intermediate one between those of the Ta and C probes,which also reflects its work function.

[0185] Next, an applied voltage was set so that the emission currentwould be constant at some voltages in a range of 1×10⁻⁵ to 1×10⁻⁴ A, toexamine the time change of the emission current. In this experiment, avariety of atmospheres was selectively used in the container in whichthe probe was placed, including a vacuum atmosphere of 10⁻⁴ Pa, a highpurity rare gas atmosphere charged at 1 atm. after evacuation of thecontainer (atmosphere 1), a high purity dry nitrogen atmosphere chargedat 1 atm. after evacuation of the container (atmosphere 2) and anatmosphere resulted from ordinary atmosphere (at a relative humidity of25% RH or so) introduced after evacuation and whose pressure had beenadjusted and set by the vacuum pump to several pressures (atmosphere 3),and a high purity oxygen atmosphere introduced at several set pressuresafter evacuation of the container to examine the influence of oxygen(atmosphere 4). When the atmospheres 3 and 4 are used in the container,the experiment was done while checking the absolute amount of oxygenusing a quadrapole mass spectrometer.

[0186]FIG. 15 graphically shows an example of the result of theexperiment effected using the probe made of C with the emission currentset to 5×10⁻⁵ A. In FIG. 15, the reference a indicates a curve of a timechange of the emission current which was when the oxygen amount in theatmospheres 1, 2, 3 and 4 is 5×10¹⁷ (mols/cm³) or less, and referencesb, c and d indicate curves of a time change of the emission currentwhich was when the oxygen amounts are shown in FIG. 15. The radius ofcurvature of the top end portion of the C probe was about 5 nm and afield is emitted from the nearly semi-spherical portion of the top endportion. In this case, the emission current density J was3.18×10⁵(A/cm²). FIG. 14 shows the deterioration of the electronemitter, having resulted in a short period of time. The experimentresult proved that also in case the C-made electron emitter excellent inoxidation resistance is used, the deterioration will be remarkable whenthe oxygen molecule density exceeds 5×10¹⁷ (mols/cm³).

[0187] When the above-mentioned value of J is substituted for J in therelational expression of X and J, defined in the present invention, theright side of the expression will be 3.98×10¹⁷, which will show that thevalue of 5×10¹⁷ (mols/cm³) acquired in the experiment is rather higherthan the upper limit of X in the relational expression. This fact showsthe nature of the carbon (C) excellent in oxidation resistance. Theresults of the experiments conducted using a variety of electronemitters and various emission current densities, which will be describedbelow, reveals that in such electron emitters and electron emitter madeof Si and on which an oxidation zone will easily be formed, therelational expression defined in the present invention should be met inorder to assure a longer service life of the electron emission source.

[0188] Taking as an index the time (td), in the characteristic curveshown in FIG. 15, in which the emission current is deteriorated to 90%of its initial value (indicated with a dash line in FIG. 15), variouselectron emitters and emission currents were examined about the relationbetween the oxygen amount in the atmosphere and the time (td).

[0189]FIG. 16 graphically shows the result of this experiment. In theexperiment, electron emission was continuously made for 10 hours andthen paused for 12 hours. This was repeated until the electron emissionhad been made for a total integrated time of 300 hours. This result isalso shown in FIG. 15. A line at which the time td exceeds 300 hours isshown in FIG. 16. The solid lines with references Si and Ta,respectively, in FIG. 16 are lines at which the time td is kept at 300hours when the electron emitters made of Si and Ta, respectively, areused. In the area under these lines, the time td is over 300 hours. InFIG. 15, the broken line indicated with the reference C indicates theresult of the experiment on the electron emitter made of C.

[0190] The line indicated with a legend “Field evaporation limit” shownat the right of FIG. 16 indicates that when the emission current densityis larger (corresponding to an emission current from a semi-sphere of 10nm in diameter being 5×10⁻⁴ A), the intensity of applied field will be10⁸ V/cm or so, meaning that the field evaporation will so be remarkablethat it will be difficult to use the electron emitters in considerationas an electron emitter. The lower limit of J indicates a lower limit “atwhich the medium can yet be heated to a significant temperature”. Whenthe high purity oxygen in the atmosphere 4 was introduced in thecontainer, the electron emitter seemed to have a longer service lifethan the line shown in FIG. 16 as compared with the service life whichwill be when an atmosphere containing moisture is introduced into theatmosphere 3., This is because the atmosphere 3 contains moisture inaddition to oxygen. It is considered that the oxygen and its dissociatedspecies as well as the moisture (water) and its dissociated speciespromote the deterioration of the emission current.

[0191] The aforementioned series of experiments revealed how theatmosphere around the electron emitter of the thermally-assistedmagnetic recording device according to the present invention should be.Based on this findings, the Invention of the present invention inventeda thermally-assisted magnetic recording device which will be describedbelow.

[0192] The construction of thermally-assisted magnetic recording headused in this embodiment of thermally-assisted magnetic recording deviceis similar to that of the first to fifth embodiments. Also, the mediumhaving previously been described concerning the first embodiment may beused as the thermally-assisted magnetic recording medium of a high Ku(Hc0) value with these heads.

[0193]FIGS. 17A and 17B are conceptual views of a part of the seventhembodiment of the magnetic recording device according to the presentinvention, showing especially a means for adjusting the atmosphereinside an enclosure of the magnetic recording device, in which FIG. 17Ais a perspective view of the enclosure and FIG. 17B is a sectional view,enlarged in scale, taken along the line X-X′ in FIG. 17A. A mediumhaving the above-mentioned magnetic characteristic was placed along withthe thermally-assisted magnetic head according to the present inventionin this enclosure, and the internal atmosphere was adjusted, thusexperimentally preparing the thermally-assisted magnetic recordingdevice according to the present invention.

[0194] In FIGS. 17A and 17B, reference numeral 70 indicates anenclosure, 71 a sealing groove, 72 a screw hole, 73 a lid and 74 anO-ring. The major part (not shown in FIGS. 17A and 17B) of the magneticrecording device which will further be described later is incorporatedin the enclosure 70. The thickness of plates used to form the enclosureis appropriately set depending upon an internal pressure of theenclosure after sealed. The plate thickness is set larger for a lowerinternal pressure to prevent the enclosure from being deformed by theexternal atmospheric pressure. To prevent such deformation due to theexternal atmospheric pressure, a honeycomb-like or rectangular cell-likereinforcing member may be attached to the plate inner wall of theenclosure or the top and bottom and right and left walls of theenclosure may be connected with some studs, instead of simply usingthick plates. When an inert gas at atmospheric pressure is charged inthe enclosure, it is not necessary to used thick plates or reinforcingmembers.

[0195] The sealing groove 71 is formed in the open end of the enclosure70 to receive the O-ring 74 therein. When the lid 73 is attached to theenclosure 70, the O-ring 74 will provide an effective sealing to isolatethe internal atmosphere from the outer atmosphere. The portion where thesealing groove is formed depends upon the design of the enclosure. Incase the enclosure formed from a rectangular parallelepiped whose fivesides are formed integrally with each other is fixed to a chassis (shownin FIG. 18) after the components of the magnetic recording device areinstalled to the chassis, the sealing groove may be provided at only oneside of the enclosure. The O-ring 74 may be a deformable ring such asrectangular ring and other ring, made of a rubber normally-used for anairtight sealing. It is fitted in the sealing groove 71. The lid 73 (orchassis) is placed on the O-ring 74 and screwed to the enclosure 70 withscrews driven into the screw holes 72, to complete the airtight sealingof the enclosure 70. Since it is only required to keep an oxygen densitydefined in the present invention for a predetermined length of time, theairtightness may not be so high as a one required for the vacuumdevices. More specifically, in case the enclosure inside is notdepressurized but an inert gas atmosphere is maintained at atmosphericpressure inside the enclosure, even a relatively simple sealing canmaintain the oxygen amount defined in the present invention for thepredetermined length of time.

[0196]FIG. 18 schematically shows a magnetic recording device disposedin the enclosure shown in FIGS. 17A and 17B, showing an embodiment of hemajor components thereof by way of example. In FIG. 18, referencenumeral 80 indicates a chassis, 81 a magnetic recording medium involvedin the present invention, 82 a thermally-assisted magnetic recordinghead involved in the present invention, 83 a high precision, high speedpositioning system and 84 a signal processing system. The inner side ofthe chassis 80 shown in FIG. 18 is nearly mirror-finished to provide asealing surface. It is closed to the O-ring 74 shown in FIGS. 17A and17B to isolate the enclosure inside from the outside atmosphere.

[0197] Alternatively, to shut off any oxidizing atmosphere, an oxygengettering substance may be provided on the electron emitter andenclosure inner wall, or a deoxidizer may be sealed in the enclosure 70.The gettering substances includes titanium or its alloy, for example.

[0198] The magnetic recording device shown in FIGS. 17 and 18 can beproduced following the procedure given below, for example:

[0199] First in a normal atmosphere (in a clean room used at an ordinarymanufacturing site), the spindle motor, magnetic recording medium 81 anda suspension arm having mounted thereon the magnetic head 82, and acontroller of the signal processing system are sequentially installed tothe chassis 80. The head has formed in the thin film element thereof theelectron beam source or emitter according to the present invention, andthe controller has additionally provided therein an electron beamcontroller (such as a voltage source, etc.).

[0200] Next, the chassis having various members installed thereon andenclosure are inserted into a glove box or sealed container charged withan inert gas, the oxygen density in the glove box or sealed container ismonitored, and the oxygen density is lowered to less than apredetermined level by circulation of the inert gas. After confirmingthat the oxygen density has been lowered to a sufficient level, a robotor human worker (in case of the glove box) assembles the enclosure andchassis together by screwing. The assembling may be done by simplewelding, not the screwing. Alternatively, a vent may be formed in theenclosure or chassis, the enclosure and chassis are assembled togetherin normal atmosphere, and then the atmosphere inside the enclosure maybe replaced with inert gas, or the enclosure may be evacuated, throughthe vent. In this case, after it is checked at the exhaust system thatthe oxygen density inside the enclosure has been, changed to thepredetermined level, a portion around the vent is sealed. For thissealing, the vent and exhaust system should be connected to each otherby a pipe formed from a spreadable metal, and after the oxygen densityhas been changed to the predetermined level, the pipe should be crimped,for example.

[0201] The thermally-assisted magnetic recording device thus constructedaccording to the present invention was tested on the stability of theelectron emitter involved in the present invention. In the test, themedium (ground potential) was rotated until the head comes to apredetermined track, then a voltage of −10V was applied to the electronemitter, and a high frequency current was supplied to the recordingmagnetic pole to write a signal of 300 kfci for example. Immediatelyafter that, the written signal was read by the GMR read element. Afterwrite to several tens of tracks, the head was sought back to the initialtrack, and a signal of 200 kfci for example was overwritten to thetrack. Just after that, the written signal was read by the GMR readelement. Write is made to several tracks, and the head was sought backto the initial track, and a signal of 300 kfci was overwritten to thetrack.

[0202] The above operations were continuously done for a time length of1000 hours. As the result, no change was found in the read signalquality, which proved the effect of the present invention. Note that ithad previously been confirmed that just supplying the same highfrequency current as in the above to the recording magnetic pole with novoltage applied to the electron emitter will not provide any recordingand heating of the medium with electron beam enables recording. Nochange in the read signal quality means that there is no change in theemission current of the electron emitter.

Eighth Embodiment

[0203] The present invention will further be described herebelowconcerning the eighth embodiment thereof.

[0204] This embodiment provides a magnetic head and thermally-assistedmagnetic recording device, using an electron emitter instead of amagnetic yoke or pole in a magnetic recording head. This construction ofthe magnetic head and thermally-assisted magnetic recording device willenable a further higher recording density.

[0205]FIG. 19 is a conceptual sectional view of the major components ofa first magnetic recording head according to the eighth embodiment ofthe present invention. The recording head shown in FIG. 19 is of aso-called single pole type. In FIG. 19, reference numeral 211 indicatesa slider base, 212 a recording magnetic pole assembly, 213 a recordingcoil, 214 a main magnetic pole, 215 a return magnetic pole, 216 aposition of medium-facing surface (air bearing surface: ABS), 217 a leadconnected to the magnetic pole assembly, and 218 a lead connected to therecording coil 213. When a voltage is applied to the lead 217, it ispossible to emit electrons from the top ends of the main magnetic pole214 and return magnetic pole 215. The lead 218 connected to therecording coil 214 is normally applied with an electric signal of adesired recording frequency, and a magnetic field modulated with theelectric signal will be applied to a magnetic recording medium (notshown) from the magnetic poles. The lead 217 may have a connection padfor itself or in common with other signal line and the like.

[0206] In this embodiment, the magnetic poles serve also as a heatingelectron emitter, so the heat source and magnetic flux emitter can beplaced extremely near to each other. As a result, an ultrahighthermally-assisted magnetic recording is enabled.

[0207] The requirements the magnetic recording head according to thepresent invention has to meet are the same as those for the conventionalmagnetic recording head except for the lead 217 provided to apply avoltage to the magnetic pole assembly 212 (or magnetic yoke).Supplemental explanation of some important components of the magnetichead according to the present invention will be given below:

[0208] Lead 217 and its pad:

[0209] The lead 217 may be a one formed by patterning a metal film suchas Cu (copper) similarly to the lead 218 provided to supply a current tothe magnetic field generating coil (recording coil) 213 for example.

[0210] The lead 217 can be connected to the magnetic pole assembly 212in the same manner as the lead 218 provided to supply a current to themagnetic field generating coil (recording coil) 213. These leads can beformed in the same process as the case may be, except for replacement ofthe etching mask. Therefore, the magnetic head can be produced at a costvery lower than the conventional magnetic head in which a laser light isused to head the medium.

[0211] A pad (not shown) may be provided to apply a voltage the lead217. This pad can simply be formed in the-same process as that for thepad used in the conventional magnetic recording head.

[0212] Top end face of the main magnetic pole 214:

[0213] In a high density HDD, since the size of the main magnetic pole214 (or magnetic yoke) in the ABS 216 is sufficiently small in size,electron emission will easily take place. However, to provide an easier,well-controlled electron emission, it has been proposed to “roughen” theair bearing surface opposite to the medium of the main magnetic pole 214(or magnetic yoke). A rough surface has many fine projections andelectric fields concentrate to the projections, so that field emissionwill preferentially take place at the projections. On the contrary, on asmooth surface, field emission point will move at the time passes, andthus cannot be well controlled. However, this will not be a greatproblem when the system requirement is such that the medium should onlybe heated within the range of the size of the main magnetic pole 214 (ormagnetic yoke) in the ABS 216.

[0214] The surface “roughness” should be such that a mean roughness Rabeing a general index obtainable through evaluation using AFM (atomicforce microscope) is over 0.5 nm and under 10 nm. A mean roughness Ra of0.5 nm or less will cause the field emission point to move-easily, whilea mean roughness of 10 nm or more will lead to a longer time for workingthe pole.

[0215] Recessing the return magnetic pole 215:

[0216] Generally, in the magnetic pole assembly or magnetic yoke of themagnetic recording head, there is provided the return magnetic pole 215(trailing-side yoke) to which the magnetic flux will come back throughthe magnetic recording medium. In the magnetic head according to thepresent invention, it is essential to head a portion to which recordingis to be made. So, field emission should not desirably take place mainlyon the return magnetic pole 215 (or trailing-side yoke).

[0217] To avoid the above, it is effective to recess the return magneticpole 215 (or trailing-side yoke) somehow from the medium-facing surface(ABS) 216 in relation to the main magnetic pole 214 (or leading-sideyoke). The recessing distance should desirably be over 0.5 nm and under1000 nm. A recessing distance of 0.5 nm or less is not suitable since itwill cause the magnetic flux not to be usable with a high efficiency,while a distance of 1000 nm or more will lead to a longer time forproducing the return magnetic pole 215.

[0218]FIG. 20 is also a conceptual sectional view showing an exampleconstruction in which the return magnetic pole 215 of a single-pole headis recessed from the ABS 216. In this example, the return magnetic pole215 is recessed over a distance R shown in FIG. 20. This recessing canbe made by patterning during production of the head, by carving byworking with FIB (focused ion beam) after forming the head or otherwise.

[0219] Surface roughness of the main and return magnetic poles:

[0220] For otherwise inhibiting the field emission from the returnmagnetic pole 215 (trailing-side yoke), it is known to roughen thesurface of the main magnetic pole 214 (or leading-side yoke) more thanthat of the return magnetic pole 215. As in the above, electric fieldwill concentrate more to rougher surface and field emission will takeplace more easily on the rougher surface. Thus, discharge from thereturn magnetic pole 215 whose surface is not so much rough will noteasily take place. Such a surface is roughened by working with focusedion beam (FIB), optimizing the etching conditions during patterning, orusing an etching pattern itself. Any of these techniques shouldappropriately be selected depending on the system requirement and cost.

[0221] Projection of the main magnetic pole 214:

[0222] For otherwise inhibiting the field emission from the returnmagnetic pole 215, it is also known to form at least one projection onthe surface of the main magnetic pole 214 (or leading-side yoke).Electric field will concentrate to the projection, so that other thanthe magnetic pole having the projection formed thereon will not emit anyelectric field.

[0223]FIG. 21 is a conceptual sectional view, enlarged in scale, of aportion, near the medium-facing surface (air bearing surface: ABS), ofthe main magnetic pole or leading-side magnetic pole of the recordinghead according to the eighth embodiment of the present invention. InFIG. 21, reference numeral 214 denotes a magnetic pole and 241 indicatesa projection. FIG. 21 shows two projections 241, but the number of theprojections is not limited to two as in this case. One projection ormore than three projections may be provided. Also the projection 241 maybe formed to be any of circular cone, square cone, triangular cone orother which would be able to emit electrons efficiently. An appropriateshape of the projection can be selected depending upon a head producingprocess. Also, in case two or more projections are provided, they mayappropriately be disposed.

[0224] It should be selected depending upon a system requirement andcost to provide a difference in surface roughness or to provide aprojection or projections. There may be provided a single projection ormore than one projection. A plurality of projections will assure abetter-controlled discharge while a single projection will contribute toa lower cost. Further, the projection may be formed by working withfocused ion beam (FIB), optimizing the etching conditions duringpatterning, or using an etching pattern itself. Any of these techniquesshould appropriately be selected depending on the system requirement andcost.

[0225] Construction of magnetic pole:

[0226] The magnetic head according to the eighth embodiment of thepresent invention is applicable to various conventional types such asring type used in an in-plane head, single-pole type used for verticalmagnetic recording, etc. as will further be described below. Any ofthese types should be selected which is most appropriate for the systemrequirement and cost.

[0227]FIG. 22 is also a conceptual sectional view of the essentialportion of the ring type magnetic recording head according to the eighthembodiment of the present invention. In FIG. 22, reference numeral 211denotes a slider base, 212 a recording magnetic pole assembly, 213 arecording coil, 221 a leading-side magnetic pole, and 222 atrailing-side magnetic pole. In FIG. 22, other elements having the samefunctions as the elements in FIG. 19 will be labeled with commonreference numerals to those for the elements in FIG. 19, and will notfurther be described.

[0228] In this variant, direction of electrons from the tip of theleading-side magnetic pole 221 toward the magnetic recording mediumenables a magnetic write to the medium being heated with the electrons.Since the heat source and magnetic flux emitter are located very near toeach other, an ultra-high density of thermally-assisted magneticrecording can be assured.

[0229] Also, in case of a ring type head, the trailing-side magneticpole 222 can be handled similarly to the return magnetic pole 215 inFIG. 19.

[0230] Protective layer:

[0231] The magnetic head according to the eighth embodiment shouldpreferably be coated with a C (carbon), B (boron) or hard oxide ornitride or a composite material containing these substances to protectthe air bearing surface (ABS) 216 since the. durability is improved.When the magnetic head is coated with C, the service life of he electronemitter used in the atmosphere is advantageously improved. Moreparticularly, 3 to 10 nm of carbon (C) should desirably be heaped as aprotective layer on the ABS 216 including the magnetic pole.

[0232] Recorder:

[0233] The thermally-assisted magnetic recording device according to thepresent invention is similar to the conventional magnetic recordingdevice except for the aforementioned magnetic recording head and a meansprovided for applying a voltage to the head.

[0234]FIG. 23 is a conceptual sectional view of the essential potion ofthe magnetic recording device according to the eighth embodiment of thepresent invention. Therefore, the elements similar to those in theconventional magnetic recording device are not shown in FIG. 23. In FIG.23, reference numeral 251 indicates a write controller to supply therecording coil 213 with a current corresponding to a recording signal,252 a voltage applicator to apply a voltage for emission of electrons tothe magnetic pole 214, and 253 a magnetic recording medium.

[0235] The voltage applicator 252 is connected to the magnetic recordingmedium 253 and magnetic pole 214. Since it is necessary to directelectrons from he magnetic pole towards the medium, the magnetic pole214 (magnetic yoke) has to be applied with a voltage which is negativein relation to the potential on the medium.

[0236] The voltage applicator 252 should further be provided with amonitor to monitor the potential difference between the magnetic pole214 and magnetic recording medium 253 to feed back the potentialdifference so that a constant or desired voltage will always be appliedto the magnetic pole 214. This is preferable since it is possible tostably write to the medium.

[0237] The voltage may be applied either continuously or in a pulsedmanner. When the voltage is applied continuously, the temperature belowthe recording magnetic pole 214 (or magnetic yoke) is always constant,which enables a stable thermally-assisted magnetic recording. Further,advantageously, the electron emission driver circuit can be simplifiedand high frequency-caused loss and induced heating will not easily takeplace.

[0238] On the other hand, when the voltage is applied in the pulsedmanner, the heat will be lost more early, and so cross-erasing will noteasily take place. Also, this pulsed application of the voltage willminimize the temperature spreading so that recorded information inadjacent tracks cannot easily be erased. Moreover, when the pulse widthis sufficiently small, the heating temperature will be constantirrespectively of the linear velocity, thus enabling a stable recordingwithout any special compensation. Further, advantageously, the pulseinterval and intensity can be modulated as necessary to arbitrarilycontrol the medium temperature and temperature spreading.

[0239] Note that the temperature elevation of the medium delays somehowin relation to the time of electron beam emission and a higher densityof recording can be attained if the delay is taken in consideration. Forthis purpose, it is an approach to provide at the trailing side of themain magnetic pole 214 the projection 241 having previously beendescribed with reference to FIG. 21. This is simple but cannot adjust somuch the distance between the heated portion and magnetically recordingportion (magnetic transition). When such an adjustment is required, itwill be effective to provide a delay between the electron emission andrecording, for example.

[0240]FIG. 24 is a timing chart showing the operations of the magneticrecording device according to the eighth embodiment of the presentinvention to emit electrons at one time while recording at any othertime. A pattern indicated with reference numeral 271 in FIG. 24represents a recording signal applied to the recording coil 213. Ittakes a simple form of 010101 . . . for the convenience of illustrationand explanation. This signal is applied to the recording coil while asignal indicated with reference numeral 272 is applied to the electronemitter. In FIG. 24, the lower side of the signal is negative, and onlywhen the signal becomes negative, electrons will be directed towards therecording medium. In this example, the timing phase is shown reversed.However, the phase difference should appropriately be set taking inconsideration a heated state of the medium and a time lag between asignal at the recording magnetic pole and developed magnetic field.

[0241] Next, the magnetic head according to this eighth embodiment ofthe present invention will further be described concerning examplesthereof:

[0242] First example:

[0243] First as the first example of the eighth embodiment, a magneticrecording head constructed as shown in FIG. 19 was produced. It was setalong with the magnetic recording medium in the spin-stand type magneticwrite and read evaluation apparatus. Separate from the magneticrecording head, a read head using a GMR (giant-magnetoresistance effect)element was also set in the spin stand. The medium was made by forming asoft-magnetic base layer of NiFe to a thickness of 100 nm on a glasssubstrate of 2.5 inches in diameter, then a magnetic recording layer ofCoPt and SiO₂ to a thickness of 20 nm on the soft-magnetic base layer,and further a protective layer of C (carbon) to a thickness of 3 nm onthe magnetic recording layer, all by sputtering, and then coating alubricant on the protective layer and removing the surfaceirregularities by tape burnishing. The magnetic recording layer has astructure having a vertical magnetic anisotropy and in which magneticparticles of CoPt having a diameter of about 7 nm are dispersed in theamorphous base material of SiO₂. The content of CoPt in the SoPt—SiO₂layer was 60% by volume. A torque meter and VSM were used to examine thethermal characteristic at different temperatures included in a range ofliquid nitrogen temperature to 500° C. The typical magneticcharacteristics measured at the room temperature were: Ku:4.5×10⁶erg/cc, Hc: 5 kOe, and Ms: 400 emu/cc. The particles having themean size was found to have a KuV/kT value of about 125 at the roomtemperature (300 K). Thus, the medium used in this embodiment can besaid to show an ambient thermal agitation at a temperature near the roomtemperature. The magnetic characteristic varied as a function of thetemperature and was found to be monotonously lower in a direction from alow temperature to a high temperature. Taking a thermal fluctuation inconsideration, the temperature dependence of the coercive force Hc0under a magnetic transition of about 10 ns was estimated. As a result,it was proved that the coercive force Hc0 at a temperature near the roomtemperature was 5.2 kOe and at a temperature of 250° C. equivalent tothe assumed recording temperature for a thermally-assisted magneticrecording effected by the magnetic recording device according to thepresent invention, the coercive force Hc0 fell to 2 kOe. When thecoercive force Hc0 at the high temperature was extrapolated, the Curiepoint was estimated to be several tens of ° C. higher than 500° C.

[0244] The medium having the above magnetic characteristic was moved ata rate of 10 m/s in relation to the head, and the write and read weretested with a relatively low linear density equivalent to a solitarywave output of 100 kfci to examine the read output voltage. The head wasmoved in contact with the slider, the spacing was controlled in a rangeof 8 to 10 nm, that is, a range from a sum (8 nm) of the head protectivelayer thickness and medium protective layer thickness to a sum (10 nm)of the lubricant layer thickness and the sum of the layer thickness. Asvariables of write and read, the emission electron current was varied bychanging voltage applied to the electron emitter and the recording fieldintensity was varied by changing the current supplied to the recordingcoil. The medium was at the ground potential.

[0245] Referring now to FIG. 25, there is graphically illustrated theresult of the evaluation. FIG. 25 shows a relation between a voltage Veapplied to the electron emitter and GMR read output voltage Vs per 1 μmof track width in which a current Iw supplied to the recording coil istaken as parameter. In FIG. 25, only two examples, Iw of 20 mA and Iw of40 mA, are shown. However, when the applied voltage Ve was lower than7.5 V, no read output could be provided with the supplied current Iwincreased to a largest possible one. On the contrary, when a voltage Veapplied to the electron emitter was higher than 15 V with the current Iwsupplied to the recording coil being 40 mA which is a practical valuefor use in the magnetic disc drive, and more preferably when the appliedvoltage Ve was higher than about 25 V with the supplied current Iw being20 mA, a high saturation read output could be provided, which provesthat the present invention is highly advantageous.

[0246] More specifically, when the applied voltage Ve was less than 7.5V, the medium was heated insufficiently or not heated by the emittedelectrons, so since the coercive force Hc0 of the medium was higher thanthe intensity of a magnetic field developed by the recording magneticpole, no recording could be made. As the applied voltage Ve exceeds 10V,the medium is more heated with the emitted electrons and thus the mediumtemperature is elevated, the coercive force Hc0 will start graduallyfalling, a recording is enabled and the read signal will startincreasing. When the supplied current Iw is yet small, the intensity ofthe magnetic field developed by the magnetic pole is low and recordingwill be enabled at an applied voltage Ve of about 20 V when the mediumtemperature is higher.

[0247] Note that in the basic example of the recording head, the lowrecording frequency was selected in order to examine the behavior of thesignal output definitely but of course this is also true for a recordingat a higher linear density.

[0248] Second example:

[0249] Next, the protective layer of the magnetic head according to theeighth embodiment of the present invention was examined about itseffect. For this examination, there were prepared a magnetic headconstructed similarly to the first example and a comparative magnetichead having no protective C (carbon) layer provided therein. Thesemagnetic heads were tested on write and read similarly to the firstexample. As the result proved, there was found no important differencein the write characteristic between the heads. However, the comparativehead crushed in about one hour after start of the experiment and nofurther experiment could be made.

[0250] The air bearing surface (ABS) of the comparative head waselaborately observed using SEM (scanning electron microscope). Manydeposits were found near the magnetic pole and the head structure wasfound partially broken. It is considered that this was caused by theabsence of the protection by the C layer. Note however that thecomparative head can be used in a magnetic recording device with alevitation of about 30 nm or when a clean atmosphere is kept in thedrive and when the medium is smooth. That is, the protective C layershould be provided depending upon a system requirement.

[0251] Third example:

[0252] As a third example of the eighth embodiment of the presentinvention, a magnetic head having the return magnetic pole providedrecessed as shown in FIG. 20, and subjected to a similar write and readexperiment to that for the first example. This magnetic head wasprepared by forming it similarly to the first example and then workingit by the FIB (focused ion beam). The recessed distance R of the returnmagnetic pole 215 was 50 nm. Owing to the recessing, no discharge tookplace from the return magnetic pole 215 and a stable discharge couldtake place. As the result, the medium noise was reduced by about 3 dB ascompared with the characteristic shown in FIG. 25. Namely, the recessingis evidently effective for a ring type magnetic head as well. Since thecost for the FIB working will add to the total cost of the head,however, it should appropriately be selected depending upon the systemrequirement whether or not the return magnetic pole is be recessed.Otherwise, the magnetic pole 215 may initially be recessed bypatterning, not by the FIB working.

[0253] Fourth example:

[0254] As a fourth example of the eighth embodiment, a magnetic head wasexperimentally prepared which had fine irregularities formed on the topend face of the magnetic face. More specifically, the similar processfor the aforementioned third example was adopted to reduce the power ofion beam during the FIB working and directing ion beam intermittentlyduring scan, thereby forming the fine irregularities on the air bearingsurfaces (ABS) of the main magnetic pole 214 and return magnetic pole215, respectively.

[0255] The magnetic head thus formed was set on the similar write andread tester (spin-stand) to that for the first example to examine thevariation of the discharge current during rotation. FIG. 26 graphicallyshows the emission current characteristic. In FIG. 26, the horizontalaxis shows a mean surface roughness Ra (nm) being a general index whilethe vertical axis shows an integration of the discharge current, as anindex of the current variation (normalized with a value which would bewhen Ra=5 nm). As seen from FIG. 26, when Ra<0.5 nm, the dischargesuddenly became more unstable. That is, when the surface roughness wasdecreased, there was found a variation of the discharge current whichseemed to have been caused by an instability of the discharging positionof the magnetic pole. On the other hand, when Ra>10 nm, the head crushedfrequently and no stable levitation was possible.

[0256] Also, a magnetic head was prepared in which Ra of the mainmagnetic pole was set to 3 nm with the intensity of ion beam variedduring FIB working while Ra of the return magnetic pole was set to 0.5nm or less (with no FIB working), and tested on write and readcharacteristics similarly to the first example. Since Ra (mean surfaceroughness) of the main magnetic pole was set to 3 nm, little instabilityof the discharge took place at the return magnetic pole. As the result,the medium noise was reduced by about 2 dB as compared with thecharacteristic shown in FIG. 25. Apparently, this treatment is effectivefor the ring type magnetic head as well. With different degrees of meansurface roughness, the test was repeated. It was found that the effectof medium noise reduction can be assured so long as Ra of the mainmagnetic pole is larger than Ra of the return magnetic pole. Since thecost for the FIF working adds to the total cost of the magnetic head,however, it should appropriately be selected depending on the systemrequirement whether the surface is to be roughed.

[0257] Fifth example:

[0258] As a fifth example of the eighth embodiment, a magnetic head wasexperimentally prepared in which the main magnetic pole had projectionsformed on the top end thereof. More specifically, the same process asfor the fourth example was adopted to control the pattern of scanningwith ion beam during the FIB working, thereby forming on the surface ofthe main magnetic pole 214 projections 241 each having the section shapeas shown in FIG. 21. Four projections 241 were formed. The magnetic headwas set in the write and read evaluation apparatus (spin stand)similarly to the first example to examine a variation of the dischargecurrent during rotation. As a result, it was confirmed that theprojections 241 contributed to the stability of discharging portion andthe variation of the discharge current could be suppressed to a levelequivalent to the standard value 1 in FIG. 26. Also, no discharge tookplace at the return magnetic pole 215 and the medium noise was reducedby about 3 dB as compared with the characteristic shown in FIG. 25.Evidently, the projections will be effective for the ring type magnetichead as well.

[0259] The projections can be formed by the FIB working as well as bypatterning during formation of the head. The patterning is advantageousin saving of the labor for the FIB working but disadvantageous in thatfine projections cannot easily be formed depending upon a process offorming the projections. It should appropriately be selected dependingupon the system requirement how to form the projections. Needless tosay, the number of the projections is not limited to four. In case asingle projection 241 is provided, the heating point is limited so thatthe single projection is preferable for a delicate heating. However, thesingle projection is disadvantageous in that the supplied power cannoteasily be increased. On the contrary, a larger number of the projections241 will enable to more positively minimize the instability of dischargebut will add more cost for the working.

[0260] Sixth example:

[0261] All techniques associated with the recording head according tothe present invention such as recessing, provision of protective layer,surface roughness adjustment and forming of a projection are evidentlyapplicable to the ring type magnetic head schematically shown in FIG.22. This is because the basic concept and effect of the provision of theelectron emitter on the magnetic pole (the magnetic pole is used to emitelectrons) is independent of the form of the head.

Ninth Embodiment

[0262] The present invention will further be described herebelowconcerning the ninth embodiment thereof.

[0263] This embodiment provides a magnetic head and thermally-assistedmagnetic reproducing device, in which the magnetic yoke or magnetic poleof the magnetic read head is used as electron emitter. This constructionwill enable high density read.

[0264] Referring now to FIG. 27, there is provided a conceptualsectional view of the essential portion of the magnetic read headaccording to the ninth embodiment of the present invention. The readhead shown is a GMR head having a so-called “yoke type” structure. Thehead is moved in the direction of arrow A in FIG. 27. In FIG. 27,reference numeral 261 indicates a GMR element, 262 a leading-sidemagnetic pole, 263 a trailing-side magnetic pole, 264 an auxiliary lead,265 a lead through which a current is supplied to the GMR element, and266 a lead to detect a voltage based on a resistance variationequivalent to a read signal. A fringing field developed from a magneticdomain of the recording medium by the yoke or magnetic pole 212 istransmitted to the GMR element 261. Note that the construction shown inFIG. 27 is just an example and a TMR (tunneling magnetoresistanceeffect) element or any one of various magnetic detecting elements may beadopted in place of the GMR element 261.

[0265] In the construction shown in FIG. 27, the voltage lead 217 isconnected to the yoke 212 to emit electrons from the yoke terminal onthe ABS and heat the recording medium (not shown). As in the eighthembodiment, the heat source and magnetic detector can be placed verynear to each other to enable an ultra-high thermally-assisted magneticread.

[0266] The detail of the thermally-assisted magnetic read is disclosedin the report by H. Katayama et al. in the Journal of Magnetic Societyof Japan, vol. 23, No. S1, p. 233, 1999.

[0267] The thermally-assisted magnetic read will be outlined below. Forexample, a ferrimagnetic alloy of an amorphous rare earth metal and atransition metal has a magnetic characteristic as shown in FIG. 28. Asseen from FIG. 28, the coercive force of the alloy will increase as thealloy temperature is elevated. At a temperature (compensationtemperature: Tcomp in FIG. 28), the coercive force will divergeinfinitely and the magnetization will be changed from one direction tothe other. Note that the compensation temperature Tcomp can be adjustedat a ratio between the rare earth metal and transition metal in thealloy.

[0268] In a medium designed for Tcomp to be near the room temperature,the magnetic domain wall after the recording will not easily move (sincethe coercive force is extremely large) and information holdingcharacteristic will advantageously increase. However, since the mediumis little magnetized in this condition, no signal can be provided evenif read by the magnetic read head. When the medium is heated up to atemperature indicated with Tr in FIG. 28 for example during reading, afringing field will take place with an intensity proportional to themagnetization at that temperature and thus the signal can be read.

[0269] According to the report by H. Katayama et al., the medium isheated by a focused laser light. This method is convenient for write ina size of about 1 μm but because of the limit of light diffraction, nomagnetic recording is possible with a high density assumed for themagnetic recording device according to the present invention. Therefore,the medium is head by electron beam. As mentioned above, the incidentelectron beam enables to heat a very small area.

[0270] Also to the magnetic read head according to this embodiment, thetechniques such as recessing, provision of protective layer, surfaceroughness adjustment, forming of the projection, etc. related to therecording head and having been described concerning the eighthembodiment are applicable as they are.

[0271] Note that the GMR element 261 and yoke 212 may possibly be inelectrical contact with each other. In case electrons are emitted fromthe trailing-side yoke 263, a current for the emitted electrons willflow to the GMR element 261. When this is a problem, the techniques suchas recessing, surface roughness adjustment, forming of the projection,etc. should be used to prevent the electron emission from taking placeat the trailing side as having been described concerning the eighthembodiment. With the auxiliary lead 264 being provided, no potentialdifference will develop across the GMR element 261 irrespectively of thepresence or absence of electron emission, and thus no current will flowto the GMR element 261. The above construction needs any working or anincreased number of leads, so it should appropriately be adopteddepending upon the magnitude of the current flowing to the GMR element261.

[0272] The magnetic read head according to the ninth embodiment willfurther be described below concerning examples thereof:

[0273] Seventh example:

[0274] A medium having a layer of a ferrimagnetic alloy (R-T) ofamorphous rare earth metal and transition metal was prepared andevaluated similarly to the first example. The medium thus formed iscomposed of a heat sink layer of Al alloy formed, recording layer ofTbFeCo, protective layer of C and a lubricant layer formed in this orderon a glass substrate. The heat sink layer was provided to adjust thethermal response of the recording layer. The composition of therecording layer was adjusted so that the coercive force at a temperaturenear the room temperature (read temperature) would have such a value ascould not be measured even by a VSM hose maximum applied field is 20kOe. The medium was set along with the thermally-assisted magnetic readhead in the spin-stand type write and read evaluation apparatussimilarly to the first example to evaluate the read characteristic.Although the medium had a recording magnetic domain formed by themagnetic recording head used in the first example, no signal could bedetected by ordinary GMR magnetic read head.

[0275]FIG. 29 graphically shows the result of the experiment on theinformation read by the magnetic read head according to the presentinvention. In FIG. 29, the horizontal axis indicates a voltage applied othe yoke while the vertical axis indicates a GMR read output voltage Vs(normalized by peak value) per 1 μm of the track width. Since the mediumis heated insufficiently or is not heated at all by emitted electronswhen the applied voltage Ve is less than 7.5 V, the medium will not bemagnetized so much as to develop a fringing field which can be detectedby the GMR element, and so no signal can be acquired. As the appliedvoltage Ve exceeds 10 V or more, the medium is heated more by emittedelectrons and the medium temperature is elevated, the magnetization willstart gradually increasing and read signal intensity will increase. Whenthe applied voltage Ve is about 25 V with which the medium temperaturewill be higher, the medium temperature is higher than Tr shown in FIG.28 and so the read signal intensity will fall. Thus, it was confirmedthat the thermally-assisted magnetic read head according to thisembodiment could detect magnetic information from a fine magnetic domainfrom which the conventional magnetic head could not read.

Tenth Embodiment

[0276] The present invention will further be described herebelowconcerning the tenth embodiment thereof.

[0277] This embodiment provides an electron beam recording devicecapable of an ultra-high density of recording even in the atmosphere orin any atmosphere approximate to the latter. This embodiment can writeand read information with a higher density to and from various mediasuch as magnetic recording medium as well as optical recording medium.

[0278] Experiment on field emission:

[0279] Before proceeding to the explanation of the electron beamrecording device according to the present invention, the experiments theInventors of the present invention conducted and results of theexperiments will be described in detail below. Namely, the Inventorsworked out the construction of this embodiment after repeating theseexperiments on the construction of the electron emitter and how theatmosphere around the electron emitter should be.

[0280] The experimental apparatus and devices the Inventors used in theexperiments are similar to those having already been described withreference to FIG. 13. As having been described concerning the seventhembodiment, the Inventors used a modified STM (scanning tunnelingmicroscopy) emitter. The STM emitter was modified in the same fourrespects and same manner as those having been described with referenceto FIG. 13. Therefore, the experimental apparatus and procedure will notbe described in detail.

[0281] First, the Inventors used carbon (C) as the material for theprobe, and made Fowler-Nordheim plotting of the I-V characteristicmeasured at atmospheric pressure.

[0282]FIG. 30 graphically shows the Fowler-Nordheim plotting of the I-Vcharacteristic. In the experiment, the interval between the probe tipand sample surface was fixed to 8 nm. Disregarding the effect of fieldconcentration at the probe tip and assuming a uniform electric field, avoltage of 1 V corresponds to a field intensity of 1.25×10⁶ V/cm.

[0283] As apparent from FIG. 30, the I-V characteristic follows theFowler-Nordheim expression when the applied voltage is 3.17 V or more,which proves that a field emission current could surely be acquired evenin the atmosphere. The emission current when a voltage of 10 V wasapplied arrived at a value as large as 61 μA which is a sufficient valueto heat the medium in the actual recording device to the recordingtemperature. The effective work function (a value resulted from divisionof the work function of a diamond-like carbon (DLC) layer by a shapeenhancement coefficient), determined from the gradient of the straightline in FIG. 30, is 0.235 eV as a uniform field. Using this value andwork function of the DLC layer (1.51 eV), the shape enhancementcoefficient α is calculated to be 6.42. This value can be said to be areasonable one since the radius of curvature of the tip of the C probeis 5 nm (thickness of the C layer coated on a Pt tip) and the intervalbetween the probe and sample surface is 8 nm.

[0284] Note that an experiment made with the probe separated more fromthe sample surface revealed that the shape enhancement coefficient wasdoubly increased with the distance being longer. This experiment resultis also reasonable since the field concentration can be considered to beremarkable with a longer interval between the probe tip and samplesurface. Similar experiments were conducted with probes made of Ta andSi in addition to the C probe. As the result, the turn-on voltage of thefield emission (a voltage with which the Fowler-Nordheim starts beinglinear) was higher than that of the C probe and the emission current wassmall. in any case, the Fowler-Nordheim plotting had a straight lineportion, which proved that a field emission took place. Carbon (C)should preferably be used to assure that application of a low voltageresults in a large field emission current.

[0285] Next, an applied voltage was set so that the emission currentwould be constant at some voltages in a range of 5 to 60 μA, to examinethe time change of the emission current. In this experiment, a varietyof atmospheres was selectively used in the container in which the probewas placed, including the atmosphere (atmosphere 1), a high purity raregas atmosphere charged at 0.5 to 1 atm. after evacuation of thecontainer (atmosphere 2), a high purity dry nitrogen atmosphere chargedat 1 atm. after evacuation of the container (atmosphere 3) and a highpurity oxygen atmosphere introduced at 1 atm. after evacuation of thecontainer (atmosphere 4).

[0286] In the atmospheres 3 and 4, the field emission current wasunstable even in a continuous operation of each of the C, Ta and Siprobes for several tens of hours. In the atmospheres 1 and 2, the Cprobe provided a table field emission current but the field emissioncurrent was lower before the time of operation reached 10 hours. Thematerial for a probe used in an inert gas atmosphere is not limited toany special one, but the carbon (C) should preferably be used to form aprobe which is to be used in the atmosphere.

[0287] Supplemental explanation will be given of the mean free path ofelectrons in an atmosphere under a pressure near the atmosphericpressure. The reason why the electron beam is used under a vacuum in theconventional TEM (transmission electron microscopy) and SEM (scanningelectron microscopy) systems is that when the electrons collide with gasmolecules, they will be scattered (elastic collision) and lose energy(inelastic collision). However, the Inventors of the present inventionworked out the fact that in case the spacing between the electron beamemitter and medium is sufficiently small, electron beam will littlecollide with gas molecules and can be incident upon the medium.

[0288]FIGS. 31 and 32 graphically show the collision cross section ofcollision of electrons in nitrogen (N₂) as a function of the electronenergy (Ee) and that of electrons in oxygen (O₂) as a function of theelectron energy (Ee), respectively.

[0289]FIG. 33 graphically shows the momentum-conversion collision rate(Pc) of electrons in H₂O (water).

[0290] In the following description, symbols Qm, Qv, Qex, Qd, Qi and Qawill appear. Qm is a collision cross section at momentum conversion(elastic collision), Qv is a collision cross section at oscillatingexcitation, Qex is a collision cross section at excitation, Qd is acollision cross section at dissociation, Qi is a collision cross sectionat ionization, and Qa is a collision cross section at adhesion. Themomentum-conversion collision rate (Pc) is a collision rate of anelectron during travel over 1 cm under a gas pressure of 1 Torr, and ithas a following relation with a collision cross section at a momentumconversion (elastic collision) (Qm):

Pc=3.54×10¹⁶ ×Qm(cm⁻)

[0291] As seen from each collision cross section shown in FIGS. 31 and32, Qm is largest. So, this collision cross section will first beexplained. This is a collision cross section of electron at momentumconversion. In the collision of an electron with a molecule, theelectron will lose little energy and change the direction of movement.

[0292] However, since the collision probability cannot easily be knownfrom Qm itself, Qm is converted to a mean free path (λ) to better knowthe momentum conversion collision cross section. The relation between Qmand λ is given by the following expression:

λ=(n×Qm)⁻¹(cm)

[0293] where n is molecular density and its value at atmosphericpressure at the room temperature (25° C.) is given by the followingexpression:

n=2.46×10¹⁹(cm⁻³)

[0294] As apparent from FIGS. 31 and 33, the momentum conversioncollision cross section (Qm) shows a largest value at Ee of about 2.5(eV) in an N₂ gas atmosphere and also at Ee of about 1 (eV) in H₂O. Witha Qm value of about 2×10⁻¹⁵(cm²) at this time, the mean free path (λ)will be about 200 nm. For example, when the distance between theelectron emitter and medium is 10 nm, the probability of collision ofthe electron emitted from the emitter with gas molecule before it isincident upon the medium can be calculated to be 5% or so (1−e^(−0.05)).This value is a one when the mean free path (λ) is shortest. As seenfrom FIG. 31, the mean free path λ is 400 nm or more except forelectrons of 1 to 4 (eV) in N₂ gas as will be seen from FIG. 31. Withthis value of λ, the collision probability of electrons will be on theorder of 2.5%. It cannot be said that no collision occurs but that theelastic collision-caused scattering loss is extremely small.

[0295] Next, the inelastic collision will be described. First, theinelastic collision of electrons in N₂ and O₂ gas atmospheres will beexplained. As seen from FIGS. 31 and 32, the collision cross section islarge in the order of Qv, Qex, Qd and Qa within a range of Ee beingabout 10 (eV). For each of these collision cross sections, collisionprobability will be estimated as for Qm. This estimation will be madeconcerning gases in which each collision cross section is large. Themaximum probability with which the electron will collide gas moleculeson a way from emission from the emitter until incidence upon the surfaceof a medium 10 nm off the emitter is estimated to be 1.2% in N₂ gas atoscillating excitation, 0.1% in O₂ gas at excitation, be 0.07% atdissociation (O₂→O+O) and 0.004% at adhesion (O₂+e→O⁻+O⁺). The energyloss of the electron at each collision is equivalent to the value alongthe horizontal axis in FIGS. 31 and 32, for example, on the order of 1to 4 (eV) at oscillating excitation and 5 to 10 (eV) at excitation anddissociation. The energy loss due to one inelastic collision is notignorable but the probability of the inelastic collision itself is verylow, so the total energy loss may be regarded as ignorably small.

[0296] The inelastic collision cross section in H₂O is unknown, but itis considered that an oscillating excitation will take place in H₂O.Also, since the energy of the dissociation of H₂O→H+OH and OH→O+H are0.2 eV and 4.8 eV, respectively, the dissociation collision should betaken in consideration. Since the collision of dissociated species withelections is stepwise, it is considered to be ignorably small. Since theionization thresholds of H and O being the dissociated species of H₂Oare 13.5 eV and 13.6 eV, respectively, the ionization of H₂O may not betaken in consideration. If it can be estimated that the inelasticcollision cross section in H₂O is same as in N₂ and O₂, the energy lossin H₂O can be judged to be extremely small.

[0297] As seen from the above, when the spacing between the electronemitter and medium surface is smaller than several hundreds of nm,electrons from the emitter will incur little scattering loss and energyloss on a way until incidence upon the medium surface. However, anexcitation collision and dissociation collision will take place but notfrequently. Practically, it will be important whether those ofdissociated species and excited species which are diffused to theemitter or medium without being recombined or de-excited will cause thedeterioration. Major ones to be taken in consideration are inert gasessuch as OH radical and O radical. Therefore, partial pressure of thesegases should appropriately be selected taking in consideration anyinfluence of them on the lubricant layer on the emitter surface andmedium outermost surface.

[0298] Static data write:

[0299] The aforementioned experiment results have proved that asufficient field emission current for heating the medium can be providedstably. Actually, a magneto-optical recording medium, phase-changerecording medium and dye layer medium were actually prepared as samples.First, STM was used to make write experiment on each of them beingstatic o relatively still in the atmosphere.

[0300] The sample was an Si wafer substrate on which a recording layerused in each medium was formed to a thickness of about 50 nm. Themagneto-optical layer was formed from a transition metal-rich layer(whose compensation point is lower than the room temperature) anduniformly magnetized with the layer directed downward. The phase-changerecording layer was initially crystallized uniformly. The write and readwas evaluated using the same apparatus as in FIG. 13.

[0301] The write test was done with the C-coated probe separated about10 nm from he sample surface, a voltage was applied in a pulsed mannerfor field emission of a current flow to heat the medium. The voltageapplied to the probe (namely, emission current value) and voltage pulseduration were taken as parameters. At each write, the sample was cannedabout 100 nm and a record mark was formed in the form of a matrix, whichwas intended for easy finding a location of the record mark in a nextmark observation test (static read).

[0302] In the write test on the magneto-optical layer, the sample wasapplied uniformly with an upward recording magnetic field of 200 Oe.Taking as parameters the voltage applied to the probe and voltageduration, a transition magnetic domain rows were defined, and then themark rows were observed using MFM.

[0303] In the test on the phase-change recording layer, the voltageapplied to the probe and voltage pulse duration were taken as parametersand amorphous marks were recorded, and then the marks were observedusing SPOM.

[0304] Also, in the test on the dye layer, the voltage applied to theprobe and voltage pulse duration were taken as parameters anddeformation of the dye layer was recorded. Thereafter, the marks wereobserved using STM switched to STM mode.

[0305]FIG. 34 graphically shows together the result of static write andread test, the field emission current I being indicated along thevertical axis while the voltage pulse time t is indicated along thehorizontal axis. In FIG. 34, the reference A indicates the result of thetest made on the magneto-optical recording layer, B the result of thetest on the phase-change recording layer, and C the result of the testmade on the dye layer. Each curve in FIG. 34 indicates a boundary of anarea above the curve in which the record marks could be found. Theresolution of the observation depends upon the means for observation butit is on the order of 10 nm. Thus, no definite observation was possibleof the record marks of less than 10 nm. The curves A, B and C in FIG. 34mean that the record marks of about 10 nm were formed under theconditions above them. When the current I is large or pulse duration tis long, the marks were large and saturated at a size of 20 nm or so. Itmeans that the spot size of the electron beam on the medium surface was20 nm or so. Since the field emission current is emitted from the tip of10 nm or so in diameter of the probe and the spacing between the probeand medium was 10 nm or so, the test results may be said to bereasonable. As having been described above, since the time of voltageapplication was relatively long in the static write test, even a currentof as low as 1 to 10 μA could form such record marks.

[0306] Dynamic write and read:

[0307] As in the above, the static write and read were successfullymade. Next, the Inventors of the present invention experimentallyprepared a recording device and operated it for recording.

[0308]FIG. 35 is a conceptual view of the essential portion of therecording head usable in the electron beam recording device according tothe present invention. In FIG. 35, reference numeral 301 indicates ahead substrate, 302 a emitter electrode layer, 303 an insulative member,304 a gate electrode, 305 an emitter, and 306 a voltage source. Thesurface of the gate electrode layer 304 in FIG. 35 works as the airbearing surface (ABS), namely, a surface opposite to a medium duringmagnetic recording.

[0309] The substrate 301 should preferably be formed from an ALTICsubstrate used as a magnetic head slider or an ALTIC substrate having anSi wafer joined thereon. In the latter case, the emitter can be formedby surface orientation selective etching of Si material. The emitterelectrode 302 may be formed from any conductive material but preferablyfrom Cu (copper), Al (aluminum), Au (gold), Ag (silver) or an alloyusing any of them as base, which has a high electrical conductivity.

[0310] The insulative member 303 may be an dielectric material orresist, for example, SiO₂. The gate electrode 304 may not always beprovided. In a construction without the gate electrode, a voltage isapplied directly between the emitter and medium. Also in theconstruction with no gate electrode, the top end of the emitter shouldpreferably be recessed from the ABS as shown in FIG. 35 in order toprevent abrasion of the emitter top end. For a contact recording, therecessed distance will define a distance between the emitter and medium.For an levitated recording, no recessing is required.

[0311] The gate electrode 304 may be formed from a similar or samematerial as for the emitter electrode 302. The emitter may be formedfrom any material which is capable of field emission of electrons, andpreferably from Ta, Si or C, and more preferably, from C (DLC).Alternatively, a suitable metal may be worked to be a cone and DLC becoated to a thin layer on the cone. The voltage source 306 may be eitherDC or pulsed one, or a modulated one. In the last case, it is should bemodulated to prevent variation of emission current due to variation oflevitation, or record mark size is multivalued for a higher density ofrecording.

[0312] The electron beam recording head constructed as in FIG. 35 can beconstructed as in the following. First, the emitter electrode layer 302is formed on the ALTIC substrate 301 by sputtering or evaporation, andworked to a predetermined pattern by etching. The predetermined patternmeans electrical connection between the emitter electrode and emitterand leading of the emitter to a pad for connection to the voltage source306.

[0313] Next, the insulative member 303 is formed by sputtering,evaporation, CVD process or the like. For using a resist as theinsulative member 303, the spin coating is employed. Next, the gateelectrode layer is formed by sputtering or evaporation, and then issubjected to PEP process in which a gate electrode on which an emitteris to be provided and an insulation under the electrode are removed byetching. The insulation may be removed by anisotropic etching orisotropic etching. In the latter case, a cavity will be formed near aworking hole for the gate electrode. A construction using no gateelectrode, the gate electrode portion may be formed from any materialother than electroconductive material, and the material may be the sameas for the insulative member 303.

[0314] Next, the emitter material is formed by sputtering. For example,by sputtering with an appropriate anisotropy from above the gate, aconic emitter can be formed spontaneously owing to “shadowing effect”peculiar to sputtering. The “shadowing effect” is such that a layerformed on the top of he gate 304 by sputtering will grow in the form ofa debris from around the gate hole towards center and the emitter willgrow on the emitter electrode behind the debris.

[0315] Next, the emitter layer is removed from the gate by CMP (chemicalmechanical polishing) for example. Then, with the pads of the emitterand gate electrodes being exposed, Au is grown on the pads by frameplating to form terminals. After that, the terminal was cut into chipsand each chip was worked into a slider. The chip was assembled by headgimbal assembling, the terminal was connected to the lead from thevoltage source to complete the recording head installable in theelectron beam recording device according to the present invention.

[0316] The present invention is not limited to any special head type butit may be applied to a so-called planer type head in which a filmelement is formed on the lateral side of a slider, a head prevailing inthe current field of he magnetic recording head and in which a filmelement is formed on the rear end face of a slider, or to a head inwhich an electron beam source is attached to a slider with a PEPprecision. For example, the electron emitter may be formed on thelateral side or rear end face of a slider by using a wedge-like mask tomake an oblique sputtering, thus forming a DLC layer on the wedge-likemask (whereby an emitter having a sharp tip formed owing to the“shadowing effect” can be formed), or by sharpening the tip of anemitter, once formed, by FIB working for example at the later stage ofprocess.

[0317] In addition to forming an emitter directly on a slider in thelayer or film forming process, the following method is also possible.Namely, a convex pattern is formed on a slider substrate with aslider-size pitch, then a concave pattern corresponding to the convexpattern the slider substrate is provided on a substrate on which theemitter is to be formed, and the substrates are joined to each other andchipped to provide the emitter.

[0318] The electron beam recording according to the present inventioncan be effected as in the following with the recording head formed as inthe above being installed to a head of the spin-stand type magneticwrite and read evaluation apparatus for example.

[0319]FIG. 36 is a sectional view of an example of the recording mediumusable in the embodiments of the present invention. In FIG. 36,reference numeral 307 indicates a medium substrate, 308 a seed layer,309 a recording layer, and 310 a protective layer. The construction ofthis medium varies from one reading method to another. The constructionshown in FIG. 36 is suitable for a probe type reading as in theaforementioned static write and read test. When a near-field light isused for an optical reading, the construction should be of an opticalinterference type similarly to that used in ordinary optical discs.

[0320] In any case, it is important that for writing, the electronemitter and medium should be placed near each other with a distancesmaller than the mean free path of electrons in the operatingatmosphere, and that for reading with a high resolution, the probe ornear-field light source and medium should be disposed near each other asin the writing.

[0321] The medium substrate 307 may be formed from glass, Si orpolycarbonate, and address information, servo control information, etc.may be formatted by either pre-formatting or soft-formatting.

[0322] The pre-formatting may be such that pre-pits and pre-grooves areformed in the medium substrate by the 2P process for example, or in caseof a polycarbonate substrate, pit and land pattern may be formeddirectly in the substrate by injection molding.

[0323] The seed layer 308 is not always necessary. In case aphase-change layer is used as the recording layer 309, however, the seedlayer 308 should preferably be formed from a metal layer, nitride layer,oxide layer or metal microparticle-dispersed layer to promote thecrystallization speed and control the crystal particle size. In case therecording layer 309 is formed from a magneto-optical layer, the seedlayer 308 should preferably be formed from a metal layer, metal alloylayer or the like to control the pinning site of the domain walls. Incase the recording layer 309 is formed from a dye layer, the seed layer308 should-preferably be formed from a light-absorbing metal layer or anorganic layer other than dye for promotion of deformation of the dye. Incase the recording layer 309 is formed from a magnetic recording layer,the seed layer 308 should preferably be formed from Cr or Vpolycrytalline layer to control the crystal magnetic anisotropy. In caseof a vertical magnetization recording layer, the seed layer 308 shouldpreferably be formed from a soft-magnetic layer.

[0324] The recording layer 309 may be formed from any of thephase-change, magneto-optical, dye and magnetic layers which are typicalones in the field of art. However, it is not limited to these materialsbut it may be formed from a material whose temperature can be elevatedby incident electron beams and in which some physical change will takeplace also by the electron beams.

[0325] The protective layer 310 should be formed from a ceramic and DLCsuch as oxide, nitride, carbide and boride. The protective layer shouldpreferably have coated thereon a lubricant layer used in the magneticrecording.

[0326] The medium shown in FIG. 36 can be formed by a combination ofpreformat process and sputtering process. When the medium is to besoft-formatted, it can be formed by a combination of sputtering processand soft-format process (e.g., servo write process as in magneticrecording head).

[0327] The electron beam recording head according to the presentinvention and the above-mentioned medium were tested as in the foregoingwith them set in the spin-stand type write and read evaluationapparatus.

[0328]FIG. 37 is a block diagram of the electron beamrecording/reproducing device according to the present invention, showingan example thereof. In FIG. 37, reference numeral 511 indicates adisc-shaped recording medium, 512 a spindle motor, 513 a write/read headprovided with a write electron emitter and read probe or near-fieldlight source, 514 a servo motor system to drive the head, 515 apreamplifier to amplify read signal, 516 a variable gain amplifier, 517an A/D converter to convert the amplified read signal to digital form,518 a linear-equalizer such as Viterbi decoder, 520 a data detectioncircuit to restore the read signal to original signal, 521 a decoder,522 a drive controller to control transfer of write and read data, 523an interface, 524 a circuit to drive and control the spindle motor andhead drive servo motor, 525 an electron emitter driver, and 526 amodulation circuit.

[0329] Note that the necessary components for the present invention arethe, recording system including the interface 523, drive controller 522,electron emitter driver 525, drive control circuit 524, head drive servomotor 514, recording head 513 provided with an electron emitter, mediumdrive spindle motor 512 and recording medium 511, and the othercomponents related to the reading are not essential.

[0330] In the construction shown in FIG. 37, the medium 511 is rotatedby the spindle motor 512 to guide the head 513 on which the electronemitter is formed to a predetermined recording track, and the electronemitter driver 525 drives the electron emitter to direct an electronbeam towards the medium, thereby writing data to the medium. This is thebasic concept of the present invention. In case the electron source hasa gate electrode, the driver 525 should be a one which can control boththe voltage between the emitter and gate and voltage between the gateand medium.

[0331] In the foregoing, the present invention has been describedconcerning the embodiments thereof and examples of the embodiments.However, it should be noted that the present invention is not limited tothese embodiments and examples.

[0332] For example, a structure and material of each of the elementscomposing together the electron emission source and magnetic head canappropriately be selected by those skilled in the art from thewell-known range, in addition to those having been described in theforegoing, to attain the same effect as that of the present invention.

[0333] Also, the recording medium may be a one capable of a magneticrecording, whether so-called “in-plane recording” or “verticalrecording”. For example, the recording medium may be any of varioustypes including “keepered media” having a magnetic recording layer andsoft-magnetic layer.

[0334] Furthermore, the recording medium is not limited to so-calledhard disc but may be any of other media capable of magnetic recordingsuch as flexible disc, magnetic card.

[0335] Similarly, the magnetic recording device may be a one intendedonly for magnetic write or a one intended for both write and read. Themagnetic head and medium may be disposed in a geometrical relation witheach other, such as so-called “levitated slide” or “contact slide”.Moreover, the magnetic recording device may be a so-called “removable”type one from which the recording medium can be removed.

[0336] While the present invention has been disclosed in terms of thepreferred embodiment in order to facilitate better understandingthereof, it should be appreciated that the invention can be embodied invarious ways without departing from the principle of the invention.Therefore, the invention should be understood to include all possibleembodiments and modification to the shown embodiments which can beembodied without departing from the principle of the invention as setforth in the appended claims.

[0337] The entire disclosure of Japanese Patent Application No.H11-375042 filed on Dec. 28, 1999 including specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A thermally-assisted magnetic recording devicecomprising: an electron emitter configured to. emit electrons toward amagnetic recording medium for heating a recording portion of themagnetic recording medium to decrease a coercive force; and a magneticpole configured to apply a magnetic field to the magnetic recordingmedium to record an information magnetically to the recording portiondecreased in coercive force.
 2. The thermally-assisted magneticrecording device according to claim 1, wherein the electron emitterheats the magnetic recording medium so that a coercive force of therecording portion of the magnetic recording medium becomes smaller thanan intensity of the magnetic field developed at the recording portion bythe magnetic pole.
 3. The thermally-assisted magnetic recording deviceaccording to claim 1, wherein at an ambient temperature, the recordingportion of the magnetic recording medium has a larger coercive forcethan the intensity of the magnetic field developed by the magnetic pole.4. The thermally-assisted magnetic recording device according to claim1, further comprising a driving mechanism configured to move themagnetic recording medium in relation to the electron emitter and themagnetic pole, wherein the electron emitter is provided at a leadingside of the direction of the movement by the driving mechanism and themagnetic pole is provided at a trailing side of the direction of themovement by the driving mechanism.
 5. The thermally-assisted magneticrecording device according to claim 4, wherein the electron emitterincludes a plurality of electron emitting portions disposed along adirection of the movement thereof by the driving mechanism.
 6. Thethermally-assisted magnetic recording device according to claim 4,wherein a recording track parallel to the moving direction is formed onthe magnetic recording medium; and a length Te of the electron emitterin a width direction of the recording track and a length Tw of themagnetic pole in a width direction of the recording track are in arelation of Te/2≦Tw≦2Te with each other.
 7. The thermally-assistedmagnetic recording device according to claim 1, wherein the electronemitter emits the electrons by field emission.
 8. The thermally-assistedmagnetic recording device according to claim 1, wherein the electronemitter emits the electrons in a non-oxidizing atmosphere ordepressurized atmosphere.
 9. The thermally-assisted magnetic recordingdevice according to claim 8, the oxygen partial pressure X (in mols/cm³)and emission electron current density J (in A/cm²) of around theelectron emitter are in relations of X≦1.25×10¹²×J and J≦10⁴ with eachother.
 10. A thermally-assisted magnetic recording device comprising: arecording magnetic pole configured to apply a magnetic field to amagnetic recording medium; and a lead connected to the magnetic pole;wherein a voltage is applied to the lead to allow the magnetic pole toemit electrons with which a recording portion of the magnetic recordingmedium is heated, and information is recorded magnetically to themagnetic recording medium by applying the recording portion with amagnetic field from the magnetic pole.
 11. The thermally-assistedmagnetic recording device according to claim 10, wherein the mean valueof the surface roughness of the magnetic pole opposite to the magneticrecording medium is over 0.5 nm and under 10 nm.
 12. Thethermally-assisted magnetic recording device according to claim 10,further comprising a return-path magnetic pole forming a magneticcircuit for the magnetic field with the magnetic pole and magneticrecording medium; the return-path magnetic pole being located asrecessed from the magnetic pole as viewed from the magnetic recordingmedium.
 13. The thermally-assisted magnetic recording device accordingto claim 10, further comprising a return-path magnetic pole forming amagnetic circuit for the magnetic field with the magnetic pole andmagnetic recording medium, a mean value of the surface roughness of thereturn-path magnetic pole opposite to the magnetic recording mediumbeing smaller than a mean value of the surface roughness of the magneticpole opposite to the magnetic recording medium.
 14. Thethermally-assisted magnetic recording device according to claim 10,wherein the magnetic pole has at least a projection provided on asurface thereof opposite to the magnetic recording medium.
 15. Athermally-assisted magnetic reproducing device comprising: a magneticyoke; a lead connected to the magnetic yoke; and a magnetic reproducingelement magnetically coupled to the magnetic yoke; wherein a voltage isapplied to the lead to allow the magnetic yoke to direct electronstowards a magnetic recording medium to heat the magnetic recordingmedium, and information is reproduced from the magnetic recording mediumby guiding a magnetic field from the magnetic recording medium to themagnetic reproducing element via the magnetic yoke.
 16. Thethermally-assisted magnetic reproducing device according to claim 15,wherein a mean value of the surface roughness of the magnetic yokeopposite to the magnetic recording medium is over 0.5 nm and under 10nm.
 17. The thermally-assisted magnetic reproducing device according toclaim 15, further comprising a driving mechanism to move the magneticrecording medium in relation to the magnetic yoke; the magnetic yokeincluding a first magnetic yoke provided at a leading side of thedirection of the movement by the driving mechanism and a second magneticyoke provided at a trailing side; and the second magnetic yoke beinglocated as recessed from the first magnetic yoke as viewed from themagnetic recording medium.
 18. The thermally-assisted magneticreproducing device according to claim 15, further comprising a drivingmechanism to move the magnetic recording medium in relation to themagnetic yoke; the magnetic yoke including a first magnetic yokeprovided at a leading side of the direction of the movement by thedriving mechanism and a second magnetic yoke provided at a trailingside; and a mean value of a surface roughness of the second magneticyoke opposite to the magnetic recording medium being smaller than a meanvalue of a surface roughness of the first magnetic yoke opposite to themagnetic recording medium.
 19. The thermally-assisted magneticreproducing device according to claim 15, wherein the magnetic yoke hasat least a projection provided on a surface thereof opposite to themagnetic recording medium.
 20. An electron beam recording devicecomprising an electron emitter configured to emit electrons towards arecording medium in a gas atmosphere at a substantial atmosphericpressure to heat the recording medium and to record information to therecording medium, wherein the electron emitter and recording mediumbeing spaced from each other by a distance shorter than the mean freepath of the electrons emitted from the electron emitter.
 21. Theelectron beam recording device according to claim 20, wherein theelectron emitter emits electrons by field emission.
 22. The electronbeam recording device according to claim 20, wherein the electronemitter has a surface layer formed mainly from carbon.
 23. The electronbeam recording device according to claim 20, wherein when a spacing d(in nm) between the electron emitter and recording medium meets thefollowing condition: d<λmin×(760/P) where λmin is the minimum value (innm) of the mean free path of the electrons at 1 atm. and P is thepressure (in Torr) of the gas atmosphere.
 24. The electron beamrecording device according to claim 20, wherein the recording medium hasa recording layer whose optical characteristic changes as it is heated.